I've had a mk5 and a mk6 RS2000 4x4. The engine is the old I4 from the sierra so a bit heavier than a zetec and not many tuning options (unless you turbo it yourself like I did). They are appreciating rapidly now too, if you can find a 4x4 you'll be very lucky.
These are firming up in value, but it seems not everyone believes they should. That said, I doubt many are around now and many like other cars including the MG Metro Turbo have been the subject of engine donors for other cars.
I've driven a few MkVs and whilst they weren't Ford's finest hour, they're alright. They're practical, cheap to fix, easy to work on and and alright steer. I'd hope an RS2000 4x4 would be much nicer but I can't comment. They do have some kudos about them ; they're not just another Escort GTi ; the engine has more poke for one, and it is different as pointed out.
Rust and parts availability would be my worries. 80s Fords are now a real pain to get decent parts for, and it wouldn't surprise me if 90s models have gone the same way ; after all, when did you last see a 90s Ford on the road, bar maybe a Ka?
I bought one for £200 about 6 years ago. I only wanted it to put the engine in my mk1. It had been off the road for 2 years and was absolutely rotten. The hinged panels were all good but the shell was ripe. I kept the bonnet, bumpers, spoiler, binnacle and steering wheel incase they can make me rich one day in the future
Regarding the engine, it's pretty lively in my mk1. A cheap way to get 150bhp. There is a company in castlecombe that change the chip in the ecu and remap for £500. They reckon they can get 165-170 from a stock motor depending on condition. It can also then be remapped to run with the 2.3 Galaxy bottom end. They give huge torque.