Thoughts re: cartridge/interconnects

My "system" is about 10 years young and comprises a Linn LP12 with Sumiko Premier FT3 with a Linn K18 cartride; CP SA-3000 & SA12, Vandersteen 2C's, interconnects are MI 330's. Because I live in a small market which has only one store which carries cartriges, your recommendations/suggestions would be appreciated. I'm not enthralled with the cartridge. Thoughts about a cartridge under $500 for the system. The local dealer carries only Krado. Secondly, the interconnects and tubes in the amps are from the original date of purchase. Any recommendations on (1)better interconnects and (2) replacing the tubes in the amp. The SA12 works; no tubes are blown, should they be changed just because they are "OLD"? My girlfriend may want to change me. Thanks for your feedback. Golfnrob@aol.com