Wojo - there is no Rega merry go round. You must be thinking of Linn. Their LP12 has an option list like a Porsche. I've heard
Rega is pretty clear- with each rung up the ladder you get a better arm (usually) a better power supply (usually) and better platter (I think always). Cartridges are separate, but packaged with a discount. I don't buy the Rega cartridges, because they would be better with a Rega phono stage, and I p/refer flexibility.
AJ - Excluding cartridges, P8 is $3100 and P10 is $5700. Even if you can get the dealer to give you all your money back from the P8, it's still $2600 more, not $2K. I know, it's the round down factor when you're buying as opposed to the round up factor when you are selling. Please let me know if you do it and your thoughts.
I wanted to keep my total out of pocket below $10K. If I ever want a very noticeable improvement, I know I will probably have to spend another $10K or more (electrostatics, subwoofer, more amp(s), P10 or Linn LP12, Lyra or Koetsu or upgraded Van den hul cartridge & phono stage) so if I can get an audible improvement under $1K at this level, I'll do it. All depends on your philosophy and how the law of diminishing returns affects you.
Now when I do get something new, it's with the mindset that I am done "for now". My amp is 15 years old, cartridge 8 1/2 (will need an overhaul or replacement within a year or so), table is a little over a year old, and when I discovered how much a phono stage would help, I got the Sutherland Insight with Linear Power Supply a month or two ago. I didn't even know how important this was until this damn virus unfortunately (or fortunately) has given me more time to think about my system and look at the Audiogon site, and discover that this was a giant step over the Phono stage in my Plinius amp that has a switch inside between MC and MM. I had always thought that it either has a phono stage or it doesn't. Furthest thing from the truth.