However, there are a couple of things that I'd ask someone new to that world to consider:
* It's trivial to point out all the ways some existing system is broken and how much better it could be given a imaginary greenfield to recreate it.
It's legitimately hard to figure out how to remediate or replace that system while keeping the business moving by scheduling downtime, training users, managing expectations, working within a budget, working within the abilities of your staff or finding new staff.
I've seen more than a few otherwise smart (typically young) people poison themselves and everyone around them by being impatient, idealistic and simply ignorant about everything beyond their own desktop.
* Doing the hard things, taking the broken stuff and making it shine builds credibility and trust. It's rare that you can come in the door and start reinventing a place, but given a solid track record - you absolutely can or at least be given the autonomy to work on more satisfying things.
* I don't have start-up experience to make a direct comparison, but I do know that the typical rates I've seen for equivalent roles in a few start-ups and even some of the prestigious SV BigCos are low to terrible relative to what's available to competent people with a track record in "enterprise".
* If you take it seriously, I think there's actually something a lot of satisfaction to be had in an enterprise. You're not racking up a million users, but you are getting a shot to change the lives of thousands if not tens of thousands of people who depend on your software and systems for their livelihood and interact with it for 8 hours of every day.