MP150 or MP200

As I have said previously the mp150 is an excellent cartridge but at present prices not sure it is THAT much better than the mp110, both of which I own and know very well.
The mp200 would likely be the next step up from the mp110 imho if not for the fairly recent price hikes .
As has been established there is a lot of competition at the $500 mark whether you go vintage or new mm/mi or even mc.

Best of luck OP, it is a tough choice at that price range but if you really like the house Nag sound then maybe the mp200 would be the right call.
YMMV

* I’m not familiar with Grace but I do know Larry Levan used them at the legendary Paradise Garage with Infinity Black Widow arm, can’t remember the model, a friend told me once, probably would have been a really sturdy cantilever. (I listen to a lot of music from that era).

No @au_lait , your friend was wrong. 
At the Paradise Garage you can only identify Stanton cartridges on Infinity Black Widow tonearms. It was American standard at that time! So you can see on this image that Larry using them. I think it was 681 series, here is more about this model.

Grace is a Japanese cartridge and for America it was an exotic. But both brads supplied phono cartridges for professional studios, radio and disco. A cantilever on all professional models is aluminum, Stanton never used any other type of cantilever (only aluminum on all models, except sapphire coated aluminum on his latest signature CS100 WOS). Grace made disco cartridges with Beryllyum cantilever and it's a huge advantage over aluminum, but for higher price! 

Grace made disco cartridges with Beryllyum cantilever and it's a huge advantage over aluminum, but for higher price! Strange that they would use beryllyium as it is a very brittle element for disco use .

@chakster I got that info personally from DJ Harvey via Francois K (who was in the booth every week)... and here is Larry himself talking about Grace carts:

“I’m going to get two more turntables so that as the night goes on, I can upgrade the sound. So I use cheap cartridges in the beginning and upgrade – I have $150 Grace cartridges which I’m really into but you can’t backcue with them. At five AM you’d say ‘what is that?’ because a record should sound as good as a tape.”

https://www.djtimspins.com/larry-levan-interview/?cn-reloaded=1