Dear NoRomance,
If the Garrard truly is as "rough in upper-mids & treble" and "lacking in detail" as many experienced users suggest....then it seems to me that putting a "Super Arm" on the table, which puts a T/T’s failings under a very severe microscope, would be casting pearls before swine?
As I may have mentioned before, the Jelco is every manufacturer’s favourite "starter" arm. Doesn’t mean that it is a bad tonearm - in fact it is extremely competent - but it is just that.
So the answer is yes, improvement is possible.
You should also have shortlisted the VPI 3D which is well within your budget. I don’t use VPI at all and I’m not on commission. ;^)
Come to think of it...does $4K not buy you a complete Prime turntable? If so I’d seriously give that some thought. :)