Join Date: Aug 2003
Bikes: '03 Fuji Roubaix Pro; '03 KleinGi Attitude; '06 Soma Rush; '04 Surly Cross-Check; '06 Soma Rush; '07 Scott CR1 / Chorus
By all means, buy the x-mart tubes. You'll probably justify your reasoning if you do this, because every time you have to replace a tube you'll be glad that you're paying less for each tube. But... you'll replace tubes far more often this way. I can speak from experience here - a friend I ride with used to insist on buying the x-mart standard and slime filled tubes. He easily had replaced ten tubes to my one through stem failures etc, and I don't recall the slime ever actually sealing a thorn puncture.
It sounds like you've had some bad luck with the thornproof tube you've installed, or you've installed it badly. I have used thornproof tubes in the past, and only ever replaced one. This was from a very sharp rock that managed to slice a 1/2 inch cut into the sidewall of the tire and stright through the tube. Never had a puncture in one. These days I mostly use standard, good quality tubes. This year I've had two punctures, both from thorns (and this is riding around in Colorado!). I have patched that tube (both times same tube) and am still using it now (I ride a road bike about 100 or so miles per week, and XC mountain bike about 20-50 miles per weekend).
IMHO, slime in a thornproof tube is overkill. I've never had a punctire from a thorn in a thornproof tube. Find the source of your leak before jumping to conclusions - it could be that the valve needs adjustment.
Patch as much as you like. My general rule is 3 patches per tube, then it gets relegated to the emergency bucket. I carry adhesive patches for use on the trail/road, and have glue patches at home. You can also use pieces of cut-up inner tube for patching, or buy the tube patch kits for automotive use (much the same as the bike patch kits, and far cheaper).