I've been doing alot of research into this recently so here goes.
The guy at the shop is somewhat right. I've seen a Dana 35 sling an axle on the street with 33's and stock gears. I have also heard of some people running the D35 with 33's and larger tires and never break an axle. If you are going to do a super 35 kit, I would put a truss on the axle as well. D35 tubes flex quite a bit and, In my experience, put un-needed strain on the axles.
Heres a bolt in 8.8, Much cheaper to prep the axle and weld on the proper brackets yourself but this is ready for install. Bolt in is nice because if they are done correctly all you do is drop the old axle out and slide the new one in. The drive shafts will be different and lines/odds and ends might need different adapters but they are pretty easy to do in your own garage(I have never done an complete axle assembly swap on a Wrangler but Have done plenty on other rigs). Bolt in Dana 44's are about the same cost.
eBay Motors: Ford 8.8 Rear Axle For Jeep Wrangler TJ YJ (item 160081149450 end time May-02-07 17:06:48 PDT)
The cheapest super 35 kit I saw was about 800 dollars, but most are a grand at least. The gears for the locker are extra in most cases. I personally wouldn't lock the dana 35 even with a super 35 kit, and I've been told by people that have them that in different situations the Forged/alloy shafts are brittle and shatter rather then just break(I have no personal experience with these and it is only hear-say from people who have them). I think it was here in WF that I saw the post that convinced me to save up for a stronger axle instead of trying to build mine. It was on the lines of, "you can build and polish a turd, but in the end it is still just a turd". D35's are good for what they were designed for, Stock 4x4's with small tires. I would Hold out and save up for a D44 or an Ford 8.8. Thats just me and my 2 cents. If you decide to build the 35 I'm sure you will get plenty of info and help here from the members. You could also Get yourself a Ford 9", A Friend of mine did this in his YJ and I am pretty sure It only ran him about 800 dollars total, with a shop welding on all the needed brackets. Anyway. Your Jeep/Your Call.
