Hi johnny ,
As Carl says this forum is all but dead now and I only look in now and then , but I may be able to help you with your question .
I have A Lingo LP12 with an Ittok lv3 and Lyra Lydian cartridge , and like you I only noticed a minimal difference when I upgraded from the Valhalla power supply to Lingo although as you say it is more convenient for speed changing .
The Ittok is a good matching arm but I preferred my old Syrinx pu2 gold tonearm but unfortunately I sold it 
.
The star of the show is the lyra cartridge but to be honest if I was considering an upgrade now I would sell my LP12 and buy something completely different ,there are so many much better turntables than the Linn available at reasonable prices .
To be honest I use my Cd player 98% of the time now and I much prefer it to my Linn LP12 ,it creates a more accurate and realistic sound and is totally fuss free .
You have a very nice amp and superb speakers so if I were you I would leave the LP12 as it is and invest your money in the best Cd player you can afford if you don't already have one 
, Cd's are so cheap now especially second hand so you can buy a whole load of music safe in the knowledge that it will last the rest of your life and as long as you steer clear of modern pop recordings the quality of most is very good and some are superb .
Here is a picture of my system.
The system is ,
Electrocompaniet EMC1 UP Cd player , EC4.7 pre , AW120 DMB power amp , PMC PB1i speakers , Linn PL12 Lingo , Ittok lv3 , Lyra Lydian , EAR 834p .
The top pictures show my old PMC OB1 speakers , the bottom has the my latest PB1i speakers next to the old OB1 .
If you live anywhere near Essex you are welcome to pop round for a listen
All the best Electro.
