If that's what you fancy doing then that's fair enough, but I'd reconsider slightly.

RS1600i side of things is fine. Little toy for the garage, all good.

But if you've got an RS1600i, then why the need for a hugely expensive and mint XR3i? Surely your "fix" for this kind of thing would come from the RS1600i?

By all means, I think the RS1600i idea is great, but £3.5k gets you a pretty decent car for everyday use nowadays, far better than an XR3i.

If I were you and wanted a mint RS1600i + a daily driver, I'd be looking at a different daily driver. Just a few examples:

-E36 328i
-E39 525i
-ST200
-MK3 Mondeo Zetec S/Ghia X
-Focus 2.0 ESP