As consumers of software, we have to get out of the mindset that we should expect something for nothing. The Planet Coaster pre-order is £20, or around half the retail price of most games at release, and assuming the game turns out to be good, that'll be excellent value for money. We should expect that Frontier support and develop the game for a reasonable amount of time after release, but at the end of the day they have a team of ~100 developers/artists/sound engineers/marketers/QA/support people working on this game, and saying "we're going to keep adding content to this game for free without a viable long-term revenue plan" would be suicidal. So I very well expect that Frontier are planning something similar to Elite: Dangerous with Planet Coaster, but hopefully with a few lessons learnt.
It's this reason why I think that UGC is going to be limited to what the game supports (i.e. blueprints for modular builds). I would hope that over the course of the year they add new rides, scenery, etc. but don't expect to see new features. I would also hope that if there is any store in the game it's limited to theming of rides and scenery. I also think that they'll aim to produce a yearly expansion (like Elite) but I hope unlike Elite they release it as something that's notionally complete rather than being worked on over the year. So, there might be a waterpark expansion, a hotel expansion, etc. and those would bring the long-term income they need to grow as a studio.
As to the price of the Early Bird edition, I can understand the thinking behind it being expensive. We went through the same thing with Elite, and generally there are two mindsets: that you shouldn't have to pay to test; or that you're getting value from being given early access. I fall into the latter camp, I found the Alpha/Beta process of Elite to be more enjoyable than actually playing the game, because I felt involved in the development process. It wasn't about finding bugs for me, but being able to give feedback on the gameplay early and often, and given the high price of entry (it was a *lot* more to get into Elite's Alpha) it limited the feedback to those who had a vested interest in the game, and importantly limited the volume of feedback.
If you fall into the group who don't like to pay to test, or if you're not happy playing something that at times will be a buggy mess, then you're not being forced to pay. You can pre-order and play when the game is released. You'll still be able to watch videos of Early Bird owners playing the game and comment on the forums. I'm very much looking forward to getting stuck in, finding what works (and doesn't) for me and helping the developers produce something that'll be enjoyed by everyone else come release time.