If you do not want to spend much money on upgrades for software you hardly use, just because you are running the latest Mac OS, try a Mac OS emulator! These are free and run nice and fast on the new Macs.
Let's take FileMaker Pro 6 for example. A piece of software I need, for a regional tree foundation I do some work for, but rarely use. And I do not want to upgrade - too expensive for the infrequent usage. So I looked at installing it on Windows in Parallels, since I have that software anyway - but that is a bit too much overhead just for running FileMaker 6. WINE did a bad job so I ditched that. Then I got a 500MHz G4 Cube! The advantage was that it runs all my older software too, like the Starwars Episode 1 Racer. But it is a bit much work turing that Mac on and off, just to do some administrative work in FileMaker 6.
So I still want to be able to run FM6 on my iMac, in Mac OS 10.8, because it is simply more convenient. I tried SheepShaver a long time ago, but then it did not work for me, somehow. But today I came across it again while searching for Mac OS emulators for Moutain Lion, and saw '2012' in the SheepShaver's blog, so that means it is still actively supported. I gave it a try and it works fantastic! And it runs my FM6 applications - and some old games, of course, like BreakThru! Really cool!
If you want to try it too, download SheepShaver and download a ROM file and the OS9 System. READ and follow these instructions and you should be ok.