That (noobs staying noobs, old content becoming irrelevant etc) happens with most any MMO as it matures though (unless it has specific design features to try and avoid it).
As to the rest, yes, alliances require commitment, but when they work, they can make small guilds more like big guilds whilst retaining their integrity.
If it helps people arrange groups for loot, rep, levelling or just plain old fun though, then it's worth trying I think...
EDIT: I meant to add, if we do ever move onto bigger instances within an alliance, then we probably would need to consider some form of DKP system, but for 10-mans, our current system should remain workable.