best upgrade for 'standard' LP12

The "midbass ripeness" is a typical characteristic of the Linn table.

Aside from the stand, which you have addressed, there is not too much that can be done without dis-assembly or the table or arm. Even re-doing the adjustment of the suspension requires some dis-assembly.

Given these guidelines, I would recommend that you get an Expressimo Audio Heavyweight drop counterweight for the RB300. This is as easy to install as your stock one. Makes a nice improvement in sound. Under $100.

If your phono section can accept it, a good MC cartridge might be a nice improvement. Like a Shelter 501. $800.

If your phono section needs improvement, that can really make the analog setup sound better. Take a look at some nice tube phono sections, that can accept low output MC carts, or a good tube MM phono section and a good Step-up Transformer. EAR and ARC make some nice ones. The Wright phono stage is real good. Probably about $1k+ for a nice one. Or consider a used tube preamp with a MC phono stage, like the MFA Magus, or Audible Illusions, or Counterpoint, or ARC SP-6. May need re-capping.

If you want to do some dis-assembly on your Linn, then you could think about some other things.

Phil, I think all your other stuff is just fine.

I have got very good results from the Heavyweight counterweight, and recommend it highly. I really did not expect alot from just a counterweight change, but it did alot more than I thought. RB300 is a good arm, and is worth upgrading in my opinion.

Trampolin might be ok, and easy.

Vibropods not needed on LP12.