It's really just a fun card. You never know what kind of deck is your opponent using or if his cards will help you win.
This may be the case if you simply throw 1 or 2 mind gates into a random deck, but I would say it's very different if you are using a deck specifically designed around it.
Assume your opponent has some sort of winning strategy(doesn't matter how effective it actually is, so long as it gives them SOME way of potentially winning the game). Once you can get to a point of having 2 or more mind gates in play and being able to use them every turn, you basically have the option of playing that same strategy your opponent is trying to use against you, except you are able to do so even faster than they are(and even this is in addition to any other cards you may have in your own deck that will give you additional ways to win). Of course, you also need the quanta to play all of those cards, but since mind gate will be giving you copies of their towers as well, this is usually not a huge problem so long as you have enough time to get things set up. Ironically though, it may be entirely possible for a mind gate deck to lose to a farm deck precisely because the farm deck does NOT have a winning strategy for you to exploit.