Opinions & guidance needed with turntable upgrade.

I am looking for opinions on upgrading my turntable. My current system consists of the following:

Pre-amp: Rogue Audio 99 with on-board phonostage
Amp: Cary Audio CAD120-S Mkii
Speakers: Totem Mani-2
Speaker Cables: MAC CuQ

The turntable is my 43 year old direct drive Yamaha YP-D8 which has been meticulously maintained and is in perfect running and cosmetic condition now running with a Dynavector 10x5, interconnecting via the original hard wired copper leads.

Please keep in mind that at 57 years old, while some systems are showing signs of their age, my hearing is still great. With that said, here are my questions.

1) What, in your opinion, would be the amount I would have to spend today to get a turntable that would perform on a par with the Yamaha? I have been given figures that range from the $400 to $1200.

2) Not being interested in a sidestep, in your opinion what would be an amount that I would have to spend to get, without going crazy, a noticeable increase in performance level, while still using the Dynavector?

3) In that price range, what makes and models of new turntables would you recommend I research?

4) In the same price range, what makes and models of previously owned turntables would you recommend I take a look at?

5) My technician recommends that should I hold onto the Yamaha, for around $400 he will eliminate the hard wired original copper connects replacing them with Cardas interconnects. If the increase in performance would be substantial, $400 sounds like a bargain but, again in your opinion, is this being pennywise and pound foolish vs. putting that money into replacing the Yamaha?

I know that these are complex environments we play with and there will more than likely be as many opinions as there are respondents, but your opinions are valuable to me as I begin my research in the upgrade.
You are clearly a meticulous person who has looked at the pros and cons. I am sort of surprised you don't have more sentimental attachment to the current table. If you do anything other than upgrade the table which I am not so sure will result in audible changes, do not sell trade or make useless this prized piece which you have owned for so long. If you want to try a modern style table with a good MC cart,
I recommend buying a VPI, you can probably get a scout fairly easily for the kind of money you have mentioned. Don't sell the Yamaha. If you can get a Superscout with a longer arm that would be even better. I don't think it will seem like a lateral move- the gimble and bearing as well as the motor and fine belt or even rim drive will all be different and your sound should be different.
Don't forget improving on your Phono Pre-amp that will also be important. None of this is cheap so save up to have the money to go for it. I also own a Music Hall MMF-5 in addition to my VPI this I think would be lateral as would be many of the under $1K tables. Clear Audio makes an entry level table for about $1250-1400, that may work as well but I would keep your very special Yamaha no matter what.
The highest value move for you would be the tonearm cable upgrade. I'd recommend a single cable set from the cartridge headshell to the RCA plugs going into the preamp.

Alternatively, somewhere around $1,200 to $1,500 you could find a used VPI or Well Tempered that I would consider a step up from the Yamaha, even with the tonearm cable upgrade.
oops...that should have read 33 year old not 43.

Mechans... I didn't say it but I am very attached to the Yamaha and would never consider parting with it. It is a dear, dear friend. I should have not used the word "replacement". Supplement would have been more appropriate.

Thank you both for your comments and insight.