New Pioneer PLX-1000 Turntable - Need recommendation for MM Cartridge and Mat

Hello A-goN'rs,

I just picked up a nearly new Pioneer PLX-1000 Turntable from a local seller. It came with an Ortofon Concorde MkII Mix cartridge and a Fluance PA-10 phono pre-amp. I set it up in my system, played around a bit with VTA and I've listened to a few records. My initial thought is that it sounds pretty darn good, especially since it is using a $99 DJ cartridge. I'm using the built-in phono pre-amp in my Rega Elicit-R integrated amp, not using the Fluance.

My reason for buying the Pioneer is to have a robust TT that I can take out of the house for an occassional music night with some local friends. It is going to work very well for that purpose. However, given how good it sounds in stock form, with the cheap cartridge, I'm wondering if a couple of minor upgrades might promote it into my main system to replace my current budget-priced belt drive table.

Does anyone have a recommendation for a <$500 MM cartridge for this TT? Also, any recommendations for a Mat that might offer an improvement in Sound Quality? Lastly, I've never owned a DD table. Regarding the platter/mat: do aftermarket mats get placed on top of the stock rubber mat? If the stock rubber mat is removed, the platter has a recess where the stock mat sits, and an elevated ring around the outside of the platter. Curious if an aftermarket mat sits on top of the stock rubber mat, or do I need to buy a replacement mat that fits in the original recess?

Thanks for your thoughts and recommendations...