Paul, I think it's mostly all been said, and +1 to all of it! Maybe especially drivetopless's "waiting until the last possible moment without incurring permanent damage is good". It's a bit of a balancing act, though I think the decisions are probably a few years away for you.
Symptoms matter a lot, for a couple of reasons:
(1) Physically, they're taken as a very strong indication that things have gotten serious or critical -- though most surgeons and many patients will tell you that a BAV can deteriorate a LOT without causing symptoms, even in us "crazy active" people! (My surgeon told me that one of the worst AVs he'd ever replaced was in a patient who scheduled her AVR so she could run a marathon first -- and mine was "in that group".)
(2) Psychologically, if you have a BAVR early, when you still feel PERFECT, you may suffer more post-op, because you won't feel THAT good for quite a while, which may seem like forever. Me, I'm 5.5 months post-op with a pretty smooth recovery, and I've just been cleared to add some jogging to my power-walking. If I hadn't torn my Achilles a year before my OHS, I probably would have been playing competitive volleyball with a bunch of 30-somethings until a few months pre-op. I hope to be playing competitive volleyball in the Fall -- ~10 months post-op -- but I won't be shocked if it doesn't turn out that way, even if everything else is fine.
All the scans and measurements matter, too, because they can help you and your team distinguish between (a) NO compensating changes or damage in your heart, (b) SOME TEMPORARY compensating changes or damage in your heart, and (c) risk of PERMANENT compensating changes or damage in your heart. In addition to the expected enlargement and wall-thickening of the Left Ventricle, and the risk of enlargement and damage (aneurysms) in the Aorta (which MAY be caused by the deteriorating BAV, but it may also be independent, caused by the same mechanisms that are gradually trashing the valve), there's also the possibility of damage to the MV, which is being overloaded with higher pressures and volumes in the LV, to compensate for the stenosis and regurg/prolapse of the AV.
In my case, some minor deficiencies (leakage/regurg/prolapse) in my MV -- which I was told would resolve naturally when the BAV was replaced with a new one -- turned into "repair or replace MV" by the time I was signing a consent form for the op, maybe 6-9 months later. In hindsight, I could very probably have skipped my MV repair (and the threat of a double-valve replacement! and also 3 months of Warfarin/ACT/INR testing) by having surgery when I still felt fine. Whether or not it would have driven me nuts to come out of "being fixed" in way worse shape than I went in, is a question for a parallel universe, not this one.
In my case, my Cardiologist was pushing me to have the op sooner, while my heart surgeon (like me) was in less of a rush. I'm doing fine the way I did it, and the other way (sooner) might have been better or worse.
Good luck! It will get worse, but then it will get fixed, and you'll be better again!