[jtkung]

To upgrade a Chibson Les Paul using reasonable but not overly expensive items, I suggest

• Replace the tuners if they are unstable. Most of the time they are good enough, however
  
• Unless the pots are scratchy or simply don't work, you don't really need to replace these or the capacitors unless you want higher reliability when gigging. 
  
• Replace the pickups
  
• Replace the bridge. The tailpiece can remain.
  

For the pickups and bridge, these are great choices:
GFS professional Series Alnico II Humbucker Nickel Case
Neck Pickup
http://www.guitarfetish.com/GFS-professi..._4156.html
$34.95

Bridge Pickup
http://www.guitarfetish.com/GFS-professi..._4154.html
$34.95

Gotoh from StewMac
http://www.stewmac.com/Hardware_and_Part...hings.html
$24.20