I am unfamiliar with your turntable, but it appears that you like it. I am familiar with the Pro-Ject you mentioned. I had Xpression II with the speed box. Xpression has a good arm, so does Rega. It was okay to begin with but I was never satisfied with it and upgraded soon enough to Nottingham Spacedeck/Spacearm used, that cost me $1400. So I would guess if you want to spend $1500 on your upgrade than perhaps it would make sense, but under $1000 probably not. Most likely upgrading your cartridge would be the most logical. What do you use now, cartridge and phono stage?
upgrade for less than $1k
I have a sweet vintage Pioneer PL-630 which is well built, has good isolation and a decent arm I imagine since it was their higher end model at the time. Can I do better with a modern TT under a grand? I had a rega P2 a while back and was dismayed at the wobbly mdf platter, plastic sub-platter and a thin particle board for a plinth. I know the RB-250 tonearm is a good one but it didn't have a chance to shine being mounted on that TT! So, is an upgrade possible for the money? I see that keeping it under $1K doesn't even get you proper speed control. How about that pro-ject xpression III with a speed box maybe?