If One Doesn't Have A Lot Of Available Funds, It's Better To Buy -

Not to sway the poll. I was not surprised when I read the results.
Generally, common notes will always be available and therefore not appreciate in value all that much.
However, it wasn't all that long ago when small portrait US Federal Reserve $5 $10 $20 $50 and $100 Notes were only worth face value and now they have appreciated in value and have some collector interest.
Common paper money also wears out and is replaced, so what is common today, may not be so common in the future. But if buying circulated and less common, always buy the most attractive and best condition you can afford.
You have to ask yourself when considering a purchase, if it is at least an attractive note that someone else would want.
If it's ugly, the next guy will probably think so too.

I didn't vote either, as I think the question should be either buy cheap UNC notes, or one better note in a better grade. I think buying poor or VG notes and expecting a good return on them should be limited to genuinely scarce material. If the premise is 'quality over quantity', then material in poor condition is not meeting the requirement. For modern 'classic' material, a very clean XF is a minimum. Not many modern notes rise in value in VF grade or lower, and it's not worth gambling on. Buy better grades.

Having said that, I've learned that the adage 'Cheap once, cheap twice' is entirely valid. What's cheap today is probably going to be cheap when it's time to sell. On the other hand, most of us collect for enjoyment, so buy what you want.

My collection consists of over 3,000 notes, all entered into a spreadsheet of identification, cost, value, numbers, etc. I update the values when new data is available, and I can tell you the 1,000 notes in my collection that are valued under $5 each represent only 3% of the collection's value. I can also tell you that only a few of those notes have migrated out to the $5-$10 value range, the next highest value category on the sheet. Probably less than a dozen. However, numerous items in the $5-$10, $10-$20, and higher categories have increased into the next higher category, or even skipped it for the next one. The $20-$50 and $50-$100 range has seen some real increases.

So if you want a bunch of inexpensive notes, fine, go ahead. But don't delude yourself as to future value. Modern notes are printed in far greater quantities than back in the 1960s, and they're destined for the packet trade. But when you think you have enough of them, do make the switch to buying fewer notes, spending your budget on quality, in better grades. You'll thank yourself in the years ahead, and if you pass your collection along, which is always a fair plan, your family will thank you, too.

I'm pretty sure I couldn't save my budget for a year and buy just one note! Buy what you want to buy, just don't delude yourself as to what you're getting, that's the main thing.

Myself, unless the deal of a lifetime presents itself, I no longer buy cheap notes. The simple reason is, I think I have enough of them, and I want to improve the collection. I've put some cheap duplicate material on ebay, and it just doesn't sell. I'm kind of resigning myself to lotting it up and selling at a loss, just for cash flow.

Always go for the best appearance in any note, centering, clean, folds, splits, all the considerations.