I have a lab with 5 routers. I recently picked up a couple of 2501's with 11.1 IOS. My question is, is it worth the 50 bucks to upgrade the DRAM and Flash so I can install 12.3 IOS? I have 2 2610XM's that will provide good functionality for practice, so I am thinking that it won't matter that much to leave the 2501's at 11.1, since they are mainly just to add hops. Will there be any problems/limitations with having an older IOS?
No, I would spend the upgrade money to buy a couple of 2600 instead even if you have to pay a few more $. They go for about $50 to $70 on Ebay.