After a while of trying to keep my toons' enhancements up to date, I figured that IOs would be more efficient - I wouldn't have to swap them out every five levels. Then, some time later, I whittled my IO usage down to three levels: 15, 30 and 45. (I decided to stop at 45 when I realized that the level-50 recipes used twice as much influence for only about a 1-2% gain, and decided that that wasn't cost-effective for my budget.)
In about the last year or two of the game, I had a lot of enhancement tables storing IOs I'd bought ahead of time at WW's, a lot of salvage racks storing salvage for recipes, and a lot of real-life paperwork keeping track of which toon needed what IOs at what level, which recipes I already had, which recipes I needed, which recipes called for which salvage, and how many of each salvage I had. I just gave up. I sold the salvage, recipes, IOs, tables and racks, and went back to replacing DOs and SOs every five turns. They did the job nicely, and were a LOT less of a headache!
And I'd happily resume keeping track of all of that headache if that were what it took to get the game back.