If you can afford to run a 3i straight away then get one!
If you want an honest answer, they're not a patch on modern cars but they're ok!
Check for rot everywhere, sills, arches, boot floor, under the bonnet [specifically around the battery tray, these rot and water can leak into the car].
The best Mk 4 XR3i is the later ones with EFi, they appeared on a G plate in 1989. They are sometimes referred to as 90 spec [at the same time there were a few changes made to the RS Turbo which people also obsess about]. Although it's the same tappety CVH, you get a better injection system, not least because if you wanted to it can be modified FAR more easily than the old Jetronics....
There were a few Mk4 models, Bonus, L GL, Ghia, XR3i, RS Turbo etc. The RS is obviously the best one by far.
We get a few Mk4's in part exchange now and then and give peanuts for them. It may be worth looking at an orion ghia 1.6i as they were the same engine as the xr3i but cheaper insurance and handled better!
I bought this gem a couple of years ago now, 1 owner and 64, 000 miles, she was totally original and a total minter
A few pics:
And tucked up nice and warm under a cover when I still had an RST: