Rewire and new power cord or Upgrade TT

First I would check rotational stability of your turntable. Improper speed will suck the life out of your records. You haven't stated a dollar figure you'd like to spend. At the least off the Basic tonearm, perhaps getting a Rega RB250 with the heavyweight counterweight and the TWL mod which will run you about $2. Everyone loves the Denon DL 103R as an audio best buy but you will need a step up device. K&K sells kits cheaply if you are handy. I doubt the power cord is an issue but while you are changing the tonearm you can swap in a new beldon piece you can pick up at a local electrical store for a few bucks. One last point. You may have a too clean belt. Wipe it down with Pledge spray wax and dust it in a plastic bag with talc. Shake it off to remove the excess and it will have the perfect amount of grip and still slip a little upon start up which increases motor life. I would not sell the existing arm or cartridge but keep it should you choose to sell the whole package and move up the food chain with a new table. You'd need to spend a lot more money to impove on the Rega and used cartridges of that quality aren't in much demand. Oh yeah, a new cable comes with the Rega.

I'm with Cmk. This A'gon member is spot on as you will not cost effectively improve the performance with cables.
And would add if you love the table and/or are being thrifty, upgrade the tonearm/cartridge.
If you can take the leap, jump into an upgrade in TT will give you the highest order of improvement overall (somewhat) regardless of tonearm/cartridge.
Would you consider a used Linn Lp12? They are in the same TT vein as what you now have and are a great used value for the sound performance. With the Linn TT deck you could upgrade as the desire and funds permit almost endlessly. Enjoy!

I agree with Cmk. Your table and arm are worthy of at least one cartridge upgrade. Not a really costly one, but something up to maybe $400 or so. Imaging and soundstaging depend on extracting clean HF and LF information from the grooves. The 1012 is pretty limited in that respect.

If your TAD-150 is relatively new it may have an MC input with enough gain for medium output MCs. Check that before deciding what kind of cartridge to buy. Most MCs image and soundstage far better than MMs.

If you're prepared to spend more, I'd go for a better rig. Getting clean HFs from cartridge to preamp before they're swamped by background noise requires a quiet, non-resonant table and arm. The physical limitations of the Thorens are probably your biggest obstacle in that respect, and rewiring won't change that.

I once considered rewiring my old H-K/Rabco ST-8. Kal Rubinson suggested it would be money ill spent, and he was right. I went for a better rig instead and the improvement was beyond my wildest dreams. Of course that broke the piggy bank, but the tunes are sure nice.

I agree with the previous posters. Upgrade the TT/arm/cartridge. Lugnut makes some very worthwhile suggestions. Before you do any purchasing of new stuff, I would take his/her suggestions to heart and embark on a tuneup of your current TT setup. Check oil in the bearing. Cartridge alignment and VTA is critical. Also experiment with mats. If, after you have cleaned and aligned everything and you still are not happy with the sound, I would next experiment with different cartridges. Dougdeacon and Lugnut suggest MCs. You might also try a Grado MM. They are inexpensive and do not require a step-up device. Grados are a standard recommendation I make to friends who are looking for an inexpensive cartridge.

I would not suggest a Grado to someone seeking better imaging and soundstaging. Grados do certain things well, but not those things.