When their sales figures get slow enough.

You can see Valheim's price history here: https://steamdb.info/app/892970/ - So you pretty much can guesstimate on when it's on sale again.

I've been playing this game regularly for more than a year now with more than 2100 hours into it. If you know where to get more entertainment than that for $20, I'd love to hear about it.

Yeah, you really can't beat that game for less than 17 Euro. That's almost a single person movie ticket and that will last you maybe 2-1/2 hours. Valheim will last much, much longer.

I would say that waiting on sale (for valheim specifically) is more detrimental to your experience than paying full price. What are you realistically going to save? 5 bucks? And for that you might be losing months (if not years) of access to a great game with a low asking price.

...but that's just my opinion.

Maybe summer sale.

Game is worth full price though. Even in Early Access and unfinished. Wouldn't be surprised to see the final price go up and the price it is now being the sale price.