Don't rush out and buy anything without thinking it through first. Just use your A1200 a bit before you decide what to do with it. With 8MB Fast RAM in your A1200, it's already quite capable of running all WHDLoad games as well as most programs and ultilities available. If I were in your position, this is the smartest thing I would do:
Keep the A1200 with 8MB RAM as your retro-gaming, classic applications machine. Take it apart and clean it if it's dirty, they can look brand new again if you use the Retr0Bright formula.
Experiment with Aros and UAE on your Mac. Go for one of the pre-installed packs like AmiKit for UAE and Icaros for Aros, which both come full of programs, utilities and games to try out, and will give you a good idea of how current the classic AmigaOS has become.
Get yourself either a G4 MacMini or a brand new Sam440/460 and install MorphOS 2.4 or AmigaOS 4.1. Either one of these computers, along with a copy of these brand new operating systems, will cost you far, far less than it would for you to upgrade an A1200 to the point where it can run earlier versions of these OSs, and both of these new machines will do the job much faster and more reliably, plus you'd be contributing back to current Amiga developers.
For your A1200, I'd recommend replacing the hard drive with a cheap IDE-CF adapter and a 4-8GB Compact Flash card, get a PCMCIA CF or SD card reader, and a PCMCIA Ethernet/Wireless card that's compatible with the Amiga. All these bits are cheap on eBay or other online shops, and with your A1200 the way it is you can still use it for a whole heap of cool things, I used mine for years like this and discovered that it's a lot more useful than many people make them out to me.
