I replaced all the sand resistors with Mills and capacitors on my SC4,s years ago and your correct they ,made a huge improvement. I did the same with my Dynaudio S25,s , replaced the sand resistor with Mills, caps with Murdoff MPK and VCap CUTF bypassed with VCap TFTF on the tweeters and WOW you will get all you say u well theaudiotweek. The Dynamics's S25,s are just stunning now.
Those of you who are wondering on the bypassing of the CUTF with the TFTF is because the CUTF is smoother more magical then the detailed TFTF, The CUTF our only avail in smaller Values so I used a 0.01 CUTF bypass with a 1.5 TFTF, this will give you the SQ qualities of the CUTF rather then the TFTF.
I hope this make sinse.