It's great if you've got the spare cash and workbench does look lovely in 1080p. Back in the day I used to use Pagestream an aweful lot - wish I had these resolutions and colour depths then.
But I've never actually managed to get any of the 3D games to go any faster (quake is still unplayable on an Apollo 060/66 + radeon 9250). Download speeds arent that much quicker through a 100mb pci card than they are through PCMCIA. You can get extra memory with some Gfx cards (I get about 224mb extra from my Radeon), but it's not as quick as having real "fast" mem. PCI networks cards also need this Gfx memory to use as buffers.
I think it's already been mentioned on the thread, but I'd definately start with an Indivision AGA and Subway first (I use old 1280x1024 lcd monitor on the Indivision). This should allow you to download and play whdload games and I find using a USB memory stick a thousand times easier than using any kind of Amiga networking to transfer files from PC or even the internet. If you've got a PC next to the Amiga like I have, then you can forget about networking and obsolete browsers forever.
And then perhaps invest in a better accelerator with more RAM. One that allows you to load custom roms into fast memory makes a massive difference to performance as well.
And a PS2 mouse adapter - maybe this should be the number one upgrade.
I think what I'm saying is that the mediator is the luxury item. It's nice, but all it gives me is a nice workbench on a nice monitor.