MikeD:
So, Softhut finally cleared out eh? They had lots of A500 stuff when I upgraded in 2002 and I thought they would still have lots left because they're so damn expensive and never lower their prices.
I hate companies that don't alter their websites to remove stuff they no longer sell. Before finding Softhut in 2002, I "added to shopping cart" lots of items on many sites (even entered credit card info!) and later found the companies actually haven't sold Amiga stuff for 8 years or more.
I eventually found my Viper 520 card in Australia - probably becuause they didn't call it a Viper and people searching wouldn't have been able to find it. Unfortunately, they went out of business in 2004. So, it seems that there are finally no companies left selling A500 upgrades.
I suggest you leave your A500 as it is and buy a new A1200 from
Amigakit (I'm getting one!). Expanding an A1200 should be much easier and you'll have a much more powerful Amiga than you would have had with an A500.