Or, keep what I have and use $ to buy more records?
In my Opinion, That is always the answer if you are a music fan and you have a limited budget. You already said you think the system sounds great. Don't muck it up. Listen and enjoy.....
I haven't heard your luxman but i suspect it's pretty awesome. i believe it's phono stage has low output MC capabilities. You might mos def wanna experiment with a few LOMC carts. I also upgraded from rotel amp/pre to a tube based amp/pre. I have found the most dramatic improvements in my system were mostly at the front end. also i agree with noromance about cables (solid core) and good support/damping for your tt.
If it moves your soul, then dont change it. If I were pushed for an answer. I would change that DL-110 on the Thornes to one of the Grado wood body Prestige cartridges $350-$600 range...They sell both low and high output ones so you can match it to your phonostage,these are all moving Iron types. This IS the cartridge for the Thornes, so I would start there. Good Luck.
I was a double stacked Advent 1970's kind of guy with an Onkyo integrated amp, Luxman TT, ShureV15 type IV cartridge.
Then, about five years ago we moved into a house with a good listening place, and I happened to hear some Maggie 1.2's and the rest was history.
Several thousand of dollars later, just once in a while, I ask myself if it was really worth it?
So...do not listen to other gear!
Buy more records!
p.s. - i had a td 166 that was heavily damped with aluminum & vinyl damping sheets / heavy brass feet (mapleshade) . sounded better than a new $1800 modern tt. i lost a lot of money when i sold the new table! i have since realized that many new tables are just tweaked out/modded old designs. check it out - http://brooklynaudiophile.blogspot.com/