ninjabee.com

Science for example...do visitors like the variety or should I always upgrade to Observatories? (i.e. 3 Obs vs. Lab, Library, Observ)

Interesting question. Visitors don't necessarily look for variety in a single category of expansions. It's way more important that you get expansions built in different expansions than it is that you upgrade within a single category. Once you've got at least some base-level expansions, then upgrading is good if there's enough time in the level for the additional expense to pay off.

Upgraded expansions have more parking space (so fewer customers turned away because they can't get what they want), and they have a higher appeal in general. So, you can make more money and hit higher station rating levels more easily with high level expansions. Just keep in mind that it takes a while to make back the money you had to spend to build the new expansion, so toward the end of a level it may not be worth it.

-- ninjabee