I work for a company that has an independent distributor arm. They pick up a few (maybe 6 to 10) films a year. I get to see a LOT of films in the budget ranges we are talking about. The difference in quality between a $50K film and a $150K film is pretty huge. The difference in quality between a $150K film and a $650K film, not so much. Maybe a slightly better grade of B/C list actor. The big difference is probably the pay scale of the people who worked on it which may or may not have much effect on the finished product.
All in general of course, always exceptions.
Although I do not work for a company, I have really close friends that do work for major distributors (theatrical) that have shingles acquiring and producing content with b/c list talent and no names at all. That's where I get my information from. Although, I can see how a small boutique could differ.
And, of course, there's the issue of eyes, and how my eyes perceive quality in comparison to others. I don't see a major difference between 50K and 100K features, and typically I only see it happen at 200K.
I also see a big difference between GH2 Hack footage, non hacked, and an incredible IQ leap from the Gh2 over the 5D (>

Purposely teasing you) but others may not see it.
Either way, it's important to know that none of it matters if you aren't creating something someone wants to actually buy.
I'd much sooner invest in a crappy horror movie that looks awesome versus a really good indie movie that looks awesome.
Yeah but isn't it common practice to lie about your budget? Those 50k budgets could very well have been 10k and the 150k could be 75k. And there is a big difference between 10k and 75k.
Absolutely. And more than likely that's what's happened.
What differences specifically between the two budget ranges are we talking about here? Better acting performances, better sound recorded on set, all of it, etc?
Another thing is, couldn't I just show distributors my movie, and not tell them how much it cost to make, and they can judge it on directing, acting, and the script, rather than the budget number?
1. It depends on what's important to you. in my case, if I had an extra 50K then it'd be better locations, better score/soundtrack, and better VFX.
2. No.