"Blue Crawler is used" <- Abyss Crawler is the only thing I've seen, and that one copy in upped SNbows that are now relatively outdated. Plus, if anything, the shard of patience RAISED the utility of Blue Crawlers as they are the puniest creature in the water decks, having low atk for a relatively high cost for such a normal vanilla attacker. This card Was, Is, and Will continue to be severely underused, even if the SoPa has made it much better (something that is the total opposite of what you said in your post. Seriously.) It was always outclassed by other cards. "Particularly after Shard of Patience" just sounds like an excuse. And please don't mix upgraded and un-upgraded copies -- these differ. If we're talking upgraded, Abyss Crawler obviously sees much more use as it becomes a great hitter.
Skeleton: Indeed, it's very cost - ineffective. Yet, I don't see anyone making a Buff This Card! for Skeleton; or I might have simply missed it. The case is, it's rarely used, and the point here is not whether it is very cost ineffective or not - I was simply going off the premise you said "You can't argue that a card that is rarely used doesn't need a buff". You're arguing -exactly- that all these cards that I mentioned -- That are, by the way, underused -- do not need a buff. Aren't you contradicting yourself a bit here..?
Anyway, back on topic. Virus and Flesh SPIDER, not Recluse, as flesh recluse outclasses our dearest mummy by one attack point, by the way -- again, don't mix Upgraded and Un-upgraded because the upgraded variant of a card may be extensively used while the un-upgraded copy may be underused -- are NOT meant to fill the role of a skeleton, not now and not ever. A flesh spider, in a rush deck, is -EASILY- outclassed by a mummy (That has one higher cost for 2 more attack.) The Flesh Spider will fit the niche of being in a Wings deck to take the webbed creatures down -- That's all (again, Un-upgraded, Upgraded I have already talked about and as I said, do not mix upgraded with un here.) A Virus would never fill the role of a skeleton in a reverse time deck effectively. So saying that they will perform "whatever role more effectively" is just around the silliest thing you could say here. Apart from their niche, every single one of these cards is outclassed by mummy in a simple mono death rush deck. By the way, nice bringing up the virus - That, too, is another underused card. Either way, all the cards you mentioned, un-upgraded, apart from niche uses, will see close to no use.
"Plague is fairly uncommon because retrovirus" No. Plague is un-upped. Improved Plague is upped. Retrovirus is also upped, and, by the way, vulnerable to CC. Plague is the only mass CC card that death has un-upgraded. Again, I'm talking un-upgraded -- If you notice, I made sure to use all of the un-upgraded names. This is not default, this is on purpose. "There is another card within the Death element that fulfills exactly the same role more effectively" False. I made sure to use all the un-upgraded names for a reason. There is no other card that fulfills Plague's role un-upgraded. Yet I don't see it being used all that much. It's underused. According to yourself, you can't argue against this. You can't argue that a card that is underused shouldn't be buffed.
"Phase spider is, again, used" In the same way that Flesh Spider is, obviously. Un-upgraded Psion outclasses it by a long shot and it will only find it's uses in the same wings deck that flesh spider will find itself nested in. Of course, Phase Recluse is, just like Flesh Recluse, a whole different story -- But, un-upgraded, un-upgraded. Aye.
Also, I find it fun that you're dismissing everything as "Other cards fulfill the same role but more effectively". Doesn't that mean that they are underused and thus should be buffed -- By your own logic, even? By the way you're saying, I could simply provide you with the response that "Earthquake fulfills the same role of Poseidon but more effectively" and end this as is.
"I still see Sapphire Chargers, but I'll admit that the Momentum/Overdrive" Overdrive is upped, we should be talking about acceleration. Just being minor here, since this isn't that big of a deal. Either way, a momentum + acceleration combo is a 2 card combo that costs 4 quanta, and will also require a third card, the creature (which by itself, un-upped, would be 3
if we want to be completely fair, since the Graviton Mercenary is the only one that would fulfill this purpose -- No one would use FireMaster for a combo that would take it's ability away.) Further on "They have indeed lost their place in the meta"; They were really never in the meta. Un-upgraded charger is underused. Again, -by your logic-, "considering how little it's used by players I don't think it can be argued that it doesn't need a change."
Blah blah blah, emerald stuff, I just decided I should point out that you said that 24 dmg for a firebolt is underwhelming. I can only assume you haven't played nor faced a firestall. At least this one you agreed it needs a rework.
"Just because something is rarely used doesn't indeed mean it needs a change." Then please don't say it does.
"However, when a unique card like this can't play a role in a mono deck, nor is it used in rainbows like the Pulverizer, it definitely deserves a buff or rework so it can become relevant."
With this last line and going off everything you've said in your relatively long post, all of the cards that you mentioned, according to you (and agreed by me on some points) will not play a big role in a mono deck as it is easily shadowed by a card that will do better in it's place. So, there is no role for this card to fill in a mono deck (In some cases, VERY literally - Skeleton, for example.) (Plague shouldn't be not counted here as it can be played but isn't -- you should develop on this more after we made it clear we're not talking about upped.). By your own logic, wouldn't these cards deserve a buff or a rework?
Disclaimer : Nothing in this post is meant to be agressive or rude, and if it came across that way then I apologize now. Also, I should further apologize for not being able to quote all that you posted. Just the thought of doing all that multiquoting and then blah blah blah when using a mouse pad that constantly fails irks me, so I avoided it and instead used these pathetic quotation marks. Again, I apologize. If this post is not replied by the time I actually get a working mouse, I'll rework it to make it look prettier. So don't be scared if any edit comes across.