the long & short of it ...

for true performance gains:
1. upgrade the 2 spool bearings - quality ABEC 5 or 7 stainless steel, not ceramics.

2. replace the stock main drag washer w/ dartaniums, extreme smoothies, or HT-100s (the last two may void shimano's warranty).

3. if line cap is not an issue - DIY poor man's wiffle spool
http://pages.infinit.net/fishing/page2.html

4. polish the copper shim under the cast control cap - about the only thing i would do from that supertuning site.

like to spend cash?
5. buy a pair of TG ceramics

6. replace the handle w/ the CTE-50GT or CTE-100GT handle

want bling?
7. replace the handle & drag star w/ those from the calais 100A

while i've tried 1 thru 6, nowadays i just stop at #2 ...