Need Advice Sota Sapphire III + SME IV arm

I recently inherited my grandfather's SOTA Star Sapphire III TT equipped with a very nice SME IV tonearm. He probably bought this back in 1989 or '90 and it was never played. He bought some Infinity IRS Beta speakers and I think he just thought he needed the best of everything to put with it - but he really just played CDs at that point.

I've never had a vacuum TT before and am debating on what to do with it. Other than needing a new cartridge everything works great! My current system is Paradigm Monitor 9s with a Rega Brio-r.

I took the table in to my local Hi-Fi store that I bought my other equipment at and they were advising me to trade it in a get something like a Rega RP-6 instead. I'm not sure how to estimate what the SOTA and SME IV would sell for but I don't think that I am getting good trade in value...

Any advise on whether to just get a new cartridge (something like a Dynavector 10x5) and keep the SOTA or should I look in to selling it and get something like the Rega P6?

Thanks for any help!
Eric