I see this play fairly often, and it always seems like a pretty fishy move to me... but villain does seem to hit an annoying amount of the time. I can understand a bluff-jam with a draw hand given the fold equity but calling just seems wreckless to me. Am I missing a trick here or should I be rubbing my hands with glee when I get called? example:

Heads Up Hyper/Hyper Turbo

Hero: Q9o on the button

Hero raises 2BB.
Villain calls.

Flop: 9s 5c 3s

Villain bets 1/2 pot.
Hero goes all in.
Villain calls and turns over Ks7s.

This is about the middle of villains range in these spots. I've seen them call with no overs, crappy gutshots, and also genuine strong draws like open enders + 2 overs.

So which sort of draws are you willing to call a jam with at 15-20BB? What about 8-12BB? Obviously it depends on the villain but what would be your baseline ranges? I tend to fold anything with less than 50% to win (e.g. <13 outs). Am I playing too tight?

easy call for villain and yes if you fold this hand you are too tight

What about the a lesser draw e.g. no overs? What are we basing this decision on? In the hand above I suppose we could say we have 2 over cards if our opponent has only made middle or bottom pair, in which case things look pretty good for us, so it's maybe 60/40 towards calling given he could also have a set or possibly 2 pair.

On the flip side, as hero in the above hand I like to play flops like this aggressively to price out draw hands as there are a lot of scare cards that can come when you have top pair on a low board. Is it better to play slower and accept he might overtake you on the turn or river? Or is fold equity still the best way to go?

Maths is extremely helpful in these situations. And it's really not very hard, try it!

I think it's the math that's confusing me somewhat. When I pokerstoved a few hands like the one above hero wins between 50 and 60% of the time... which is what I based my assumption that these were bad calls on, and why I would only call with 2 overs + flush/straight. Can you give me some examples of the math you are talking about?

Ok, math for this hand
I will assume its full stacks, so after donking flop villain has to call 21bb to win 50bb, pot odds = 42%
This hand vs your hand has 45% equity, 45% > 42% -> call

Assign a range (not a single hand) for taking the action, check your equity vs that range in a software and then compare the equity with the pot odds you get (like none888 was kind enough to explain).

Does that mean it's impossible to price out draw hands here? If the best I can do 42% vs 45% equity with a jam then his odds are only going to get more attractive if I bet smaller aren't they?

e.g. If I 3x his flop bet then he has to call 4BB to win 16 = 25% (even better).

So we should never be folding with a flush draw and one over card?

Another question this raises for me - does that mean we are both playing looser as one player's stack size decreases? E.g. If either one of us has 10BB and the other has 40, then at best I can win 20BB, so I'm calling maybe 6BB to win 20 = 30% pot odds. Therefore all I need is ~7 outs (on the flop) to call (e.g. bottom pair and one overcard)?

this is true, because of better pot odds you will have to get it in looser

Pricing out an opponent at this stack depth of a draw is indeed impossible, however that shouldn´t be your goal, if your expectation is to outplay your opponent sometimes you should try to get to turn or river, where you can make them make a mistake.
For example in the hand you played, I don´t thikn you misplayed because I expect villan to donk with bottom pair, very weak draws, and other stuff im crushing that he will call my all in with.
However let´s imagine I have a super read that this particular villain donks are 100% flush draws. Then I would not shove, I would just flat his donk, and try to make him make mistakes on turn and river if possible.