Being the hot tub n00b in the room, I'm certainly not entltled to an opinion on the relative merits of this tub vs. any other. But I am pretty qualified to speak to the general notion of repair vs. replace.
I'm cheap. Really, really cheap. I've never had much money, so I'm loathe to part with any more than I have to in order to get something I want or need done. Yet I like having the very best stuff. How does one reconcile these two conflicting pressures? By considering it a point of honour to never buy anything new unless it's absolutely necessary and unavoidable. Everything we get is used - and thus really cheap compared to new. And getting it free is even better. For me, buying new things at full price is an admission of failure and a moral stain. In the words of The Minutemen: We jam econo.
And I'm not alone in this - the entire "right to repair" movement, and repair cafes (for which I volunteer) share this ethic. It makes sense from every examinable perspective, including environmental considerations and sheer practicality. If it's broke, fix it. If it's so far gone that fixing it simply isn't a practical solution (in the short or long term), then replace it. If you can replace it with something used, that rescues a measure of triumph from the jaws of defeat.
So my question is simply this: If you're right about it just being the heater element, and (at a glance) replacement heaters are within a couple of hundred bucks, why on earth would you consider replacing the tub? Since buying our (used) tub, I've been in a few of the shops, and the prices I've seen for new tubs are bonkers.