Weight, Clamp or stabilizer?


I have a vintage Pioneer PL-560 Direct-Drive Automatic Turntable purchased around 1980. 
https://www.vinylengine.com/library/pioneer/pl-560.shtml
I'm trying to get it to produce the best sound its capable of.  I plan to order a set of SVS subwoofer feet to replace the worn feet (I have an SVS subwoofer and removed its feet and temporarily placed them on the TT base with good results).  I read an article about TT tweaks.  A few things they suggested were an upgraded mat, clamp and isolation feet.  Thing is since the TT is a direct drive I don't know how much extra weight it can take (if any), and the spindle is about 7/8 inches tall so I don't know if that's enough for a clamp.  The original rubber mat it came with is in great shape. Do I need to replace it, too? I'm willing to invest in tweaks to improve this turntable, but not interested in replacing it.
mewsickbuff
Thanks everyone. That’s a lot of information to process. Since my turntable is almost 40 years old there’s a chance a weight could be detrimental to its bearing so I’m going to pass. I’ve changed out all master sleeves, cleaned my records, and have an anti-static brush.
@ big_greg the Pioneer feet are very nice looking but out of stock and as mentioned earlier, I tried the SVS feet and heard a positive improvement.
@ chakster, I have the Shure m97xe high-performance magnetic phono cartridge. I’ve found it revealing when the album is. This is my 2nd. Bought a new one after wearing out the 1st because to my ears, it was worth it.
Still wondering about other opinions on the rubber mat.
I don't think most decent turntable bearings care much about a few ounce or a pound weight or clamp on it.  I mean a VPI Prime platter weighs 20 lbs and as you know many platters weigh a lot more.  I suspect the bearing can handle a weight just fine.
For a platter mat, you could look into the Herbies Way Excellent mat. 
They’re made extremely well and can be ordered for any turntable. I’ve had mine for a few yrs now, and I really dig it. 
You could also check out an Achromat, which are very high quality as well. 
I posted before, that I put a stillpoints clamp on my Avid Acutus Dark, and no longer do so. This is because the clamp made the sound somewhat duller ... lost its musicality and airiness. In my system is a waste of £400