Yeah, it's tricky trying to gauge how quickly to ramp things up. Last year, we felt we ramped up the difficulty too slowly with a different game, so this time we decided "short and sweet" was the way to go, but you're right, there's a preference factor there.
Your other suggestion is also a good one, I think it's something that we as devs overlooked because we'd subconsciously have a feeling for when upgrades were about to pop up (30 seconds, 45 seconds, and 60 seconds, and the screen becomes devoid of meteors right before it happens).
Thanks for the comments, and thanks for playing!!