I have in the past been very loyal to the ID Motor TT's.
Nearly 20 Years with a Garrard 401- Martin Bastin Overhauled - 9 Stone in Weight Granite Plinth, which was swapped out for a PTP Solid Nine with PTP Bearing.
I see from your post there is not a dedicated Platter Bearing Upgrade or Speed Controller referred to.
I am an advocate of the dedicated Platter Bearing Upgrades and the use of the SC.
I still own the PTP Solid Nine, but have today found the DD TT's that are overhauled with a modern design concepts for the Speed Control and Platter Bearing much more attractive to my tastes.
As for a valuation of your own TT, the SAEC has a value of approx' $550 if a price is chosen to rouse immediate interest.
The Cadenza Blue will be a difficult sale, if too much is wanted, Trade In Value and a few 100 Hours of usage life should rouse a interest?
The Beauty of the Plinth and the Value of the Plinth is in the eye of the Beholder, think maybe in the area of $150, as a means to saving a DIY Project for somebody wanting to experience this Plinth Type.
The 301 will be best assessed if looking at the Link and the Historical Sales available to be seen as well.
If it is off any interest, there are Idler Drive TT owners who own in conjunction Vintage DD TT's. Maybe this might help with your making a decision on where to look into for the next TT.