You're right about the values James, it's just gone mad.
I'll never be able to afford to get into a 3dr now.
I used to have an integrale 12-15yrs ago now, and in the last 5yrs the values have rocketed even for the very average 8v.
We've seen e30 M3s do the same of course, and now even Sunny/Pulsar GTIR's have doubled in the last few years. It wasn't long ago a £10k car was £5k.

I'm not sure if it's just the halo effect of the gpA homologation cars helping things along, but 3drs have outstripped everything in that regard, even the M3's. The RS's are very much a rich man's scene these days, and comparatively few of the original enthusiasts remain, but I doff my cap to those that have hung in there and now are sitting on a gold mine. However I pity you if you have to find spares at reasonable cost because those days are over now for sure.

I just can't get my head my 'round 'why'? Is a 3dr RS really worth 3-4x as much as nicely sorted (and appreciating) e46 M3?

Perhaps new cars aren't scratching the itch any more, but no-ones using them as daily drivers. These dealer prices are creating a panic though, where a £40k car looks like a bargain next to a £60k car..