2009 classic fuel tank issues but also gauge?

2009 Prius. Always had the classic fuel tank issues due to the bladder - lower capacity, certain pumps pumping too fast and clicking off immediately, seasonal variability in how successful gas pumping is. We always fill a bar or two before empty (before reading up about the bladder, we thought our gauge was just bad and we were always keeping tank half-full). This past week, gauge hit flashing empty on commute and I went for gas. Costco pump, started clicking immediately. I figured it surely needed at least a couple gallons, so I pumped in a few while fighting the constant clicks.

But now, gauge is still flashing empty. Tried adding gas at several other stations over the space of a few days. Same issue, constant clicking, gauge still flashing empty. A few times the gas has actually seemingly gone all the way up the filler neck and started to come out, so it does seem to be near-full, whatever the capacity is.

So, a couple questions. Is the only real fix to replace the whole $1500 assembly? I've seen posts about being able to slowly stretch the tank back out when warmer weather hits again. Second, is there a way to get the gauge working again without replacing the whole tank? I'm fine with limited capacity as long as it's at least like 5 or 6 gallons; we've dealt with that fine so far. I've tried the gauge reset instructions but had no luck.

Also, is it worth $100 to get a diagnostic from the local dealer? Will they know any more?