Eh, I view it like other discretionary income. I don't regret drinking a nice coffee or going to a film. Ok, occasionally, I regret going to a film but I usually don't think, "Wow, I shouldn't have spent money on that ticket." I just try to only go to films I like unless I'm peer-pressured by a social request. Sure, I could avoid all of that type of spending but I don't.
Anyway, I haven't really regreted anything. I always check the content of a pack and then I've done some of the sales and bundles. StrangerVille was definitely something I just got in a bundle and then I actually liked it.
I think if I were in this position, I'd try to think of ways to be less bored so that I'd feel less regret.
I will say that part of my hesitancy to go onto Sims 5 anytime soon is that I think I should enjoy the content I have as much as possible. If I'm reasonably entertained and have a nice computer then I should play with what I have. I'm sure people feel like that with TS3 and that would be me if I hadn't changed my play style into a way that is more playable in TS4. I'm just saying that I don't judge that.
I do completely understand regretting missing a sale. If in doubt, maybe take a break and then find out from social media when the sale ads come.