Many thanks for the positive responses chaps. They've been really helpful.
Upgrading to CNC level is a step too far at the moment, so I'll rule that out and stick with manual operation.
The main issue is as Jason suggests, with rough feed & backlash. I've played with the split nut block under the tables to try & reduce backlash but find that it's a very fine adjustment between a sloppy bed & binding screw which is why I thought about ballscrews.
Having scanned the various posts suggested (plus a few others), I think I'll do as you recommend and go with installing bearings & thrust races to the handwheels. A replacement, longer X axis bed was planned anyway, and it'll need a longer screw so I'll start with that. Will order a boring bar & replacement bearing block to play with. Arc is going to have a regular customer over the next few months
.
A belt drive conversion kit (mbbilici) & DRO's will be next on the list.
Once again, many thanks.
Iain.S