New cartridge $500 range

Nagaoka mp300 and above
ortofon 2m black

The Sumiko is already a pretty good $500 cartridge, I agree with others that your better bang-for-buck upgrade would be a phono stage, highly recommend the Dynavector P75 which you should be able to pick up used in that price range. Huge upgrade and tons of flexibility for loading and output.

used Dynavector P75 at $350 with dings:
https://www.usaudiomart.com/details/649701828-dynavector-p75-mk3-mmmc-phono-preamp/

hmmmmm replace cartridge or phono stage.

On one hand, upgrading a cartridge can lead to better parts: cantilever, coils, shell, diamond/stylus profile.  Just updating from the Blu Point#2's elliptical should offer significant improvements say in getting more information, better transients, fuller vocals, etc.

On the other hand, when amplifying the minute cartridge generated voltage multiple times over to get to line level, quality of parts as well as execution is also important.  One may expect better clarity, quieter background noise which leads to hearing more minute details.

Both offer sonic upgrades, but which one is best for you?

In high-end audio, many believe in the importance of the entire audio chain.  Also, many believe it's always best to address the weak link.  I too believe that your best bang for buck is to upgrade your phono stage rather than the cartridge.  That way you reduce being hampered by any future cartridge upgrades, especially if you run into a great offers like a half retail price new cartridge.

How about an Ortofon 2M Bronze.
5.5mv output. Your Sumiko is 2.5mv.
The 2M Bronze is around $440.
You said budget around $500.
If you can stretch to $750 I would recommend the 2M Black. I found it has more detail than the 2M Bronze and smoother highs. Most likely due to its shibata stylus. The stylus on either one is user replaceable.
That might be something you find important.