I guess this question belongs more properly in the screenwriters roundtable thread, but.... I have a couple of really solid ideas for tentpole/franchise type movies, that I'm passionate about, but that I've put on the backburner for now. Mostly because for a novice screenwriter, the avenues to representation (competitions, queries, etc...) seem to favor projects with far more modest budgets. Is this a wise strategy? Has any first-timer ever sold a big budget/tentpole spec script?

The answer to your last question is yes. Again it goes back to an unalterable truth: If you write a great script, nothing else matters. It will find a home in Hollywood. Practically speaking, the studio will give you a shot at the rewrite per their notes. If they feel like you didn't deliver, they will funnel the project over to established writers, so minimal risk for them. Bottom line: Take the best story concept you have and the one for which you have the most passion, then write the hell out of it.