New TT or upgrade cartridge/platter on Project DC

Use what you have.   With a collection of 150 records, it's not worth the expense.  I am old and most of my records were purchased when they were the only thing.  If I were starting out today I might buy a turntable such as yours just to play around with a bit. Going whole hog into vinyl in 2020 isn't worth the effort. Unless you are in love with music recorded prior to the early 70's, digital is better in every way.

@aasteven111: Sent a PM earlier.

I think you should upgrade the turntable. And when you do, buy your last one. They are probably the most durable of all audio equipment as nearly everything is mechanical. A $2k+ turntable won’t hold you back with the better cartridges. Cartridges make a big difference and can help you fine-tune the sound to your system. 
Because you have a Project with an integrated headshell, I suggest you try something with a removable headshell. It has the advantage of allowing you to try a wider compliance spectrum of cartridges.

I recommend the Technics 1200GR($1700)...or even the 1200G ($4k) which I own and love. The GR is understood to be 85% the sound quality of the G. They have gimbal mechanisms that are astoundingly precise. Handling the 1200G tonearm coming from an already precise 1200mk2 was a revelation. It’s like grabbing thin air.

I say go all-in on vinyl. I still buy NOS, sealed vinyl from pre-80s on eBay. And I think analogue is making small comeback in boutique recording studios. Discovering old analogue treasures is way more fun than digital. I have a ton of CDs and WAV files and an excellent CD player with 32-bit dual differential DACs but vinyl is more fun.

BTW, owning 150 albums was also my breakthrough moment. I started late...but in a few years I now have 900 great albums and counting. The world is too full of reasonable people.

@aasteven111
I was in a very similar position as you, and also decided on a Pro-Ject Debut Carbon for exactly the same reasons.

I immediately replaced the Ortofon Red with a Grado Red, and soon after purchased the acrylic platter. Both were/are good improvements, but also cost $300 +/-. So, $675 +/- overall invested afterwards (bought the Debut as an open box). Still, not a bad ‘starter’ setup all things considered.

In my case, I needed a phono pre, so again, for cost and not sure if returning to vinyl would stick, bought a Schiit Mani. Great pre for the money, but now thinking of an upgrade, or purchase a linear power supply for the Mani.....but believe an overall upgrade would be money better spent.

Well, as you, I have probably purchased almost as many new (used) albums in a short period as I had total during the 60-70’s before moving to digital in the 80’s. Seriously. The return of vinyl in my system is here to stay long term. So, now I think had I realized that, I may have been better off buying a VPI Scout, or similar. But, it’s OK, it’s all part of the journey, it took a small investment to begin thinking of a larger one, and I now have a much better idea of what may be important in taking that step.

So, right now, I’m now thinking of a tube phono stage next, but really, probably won’t put more money into that table, including another cartridge, as I think the table itself is becoming the ‘weak link’. Thus, I will make any further decisions with another table in mind first. Another table/arm may make a cartridge upgrade/decision now an ill advised move. I have no big issues with the Grado in my current set-up. And I’m also keeping that in mind with a new phono pre as well.

It became clear to me rather quickly, that to have a really nice vinyl set-up takes a lot of cash. I just have not figured out how much I’m ultimately willing to invest. But the amount is more than I’ve already spent, for sure. Regardless, I’m enjoying the journey.