If fluctuations are truly random, then you will end up with each copy having the average of the combined average att and hp...
eg.
If you had one uppded and one unupped in play, then over time everything will average out to being (4+7)/2 | (4+7)/2 regardless of upped or unupped status... this means that the upgraded version should either be cheaper or have greater total stats. Otherwise there is no reason to upgrade it.
By the way, will fluctuations allow interchange between att and hp or will hp and att be on seperate fluctuations.
E.g. could two 4|7 fluxors fluctuate to, say, a 5|6 and a 6|5 (which would require transfer of hp to att)?
If this is the case then it makes buffs or damage / debuffs to att and hp essentially equivalent... which would certainly be quite unique.