Two quick questions

There will be a demo not long after 1.03 is released (hopefully end of this week or so).

You'll probably get a lot of varying answers on your first question - moving the game to blend with RTS cut out some depth from traditional RTS genre. Diplomacy is going to be worked on, and so is the AI. If you're worried about game speed, you can still have slow-going games, Sins definitely didn't dumb everything down to a click-fest.

Myself, I like GalCiv2, Sword of the Stars (just started learning it actually :P) and I love Sins.

Don't know about the demo, but as to suitability for you, I know I loved both MOO and MOO2, as well as GalCiv, and I think you would like Sins. If you are concerned about the speed, don't be, as Sins generally leaves you with sufficient time to think and react. If fact, if you read the boards much, you will find several RTS players who say the pace of play is too slow, even at the highest speed. The three races are sufficiently different to give you many hours of enjoyment.

I'm not a fan of turn based games so I normally set Sins on fast or even + up my speed to 2x or 4x during slow periods of gameplay. This only works in single player though and I have played a lot of RTS games in the past. If you don't like such a pace you can slow sins down as slow as you want it to go. If you set the game speed down to slow it's...well, very slow. The addition of being able to pause helps if you really need extra time to give commands. Sins can be fast or slow depending on how you set up the match. It's very flexible in that regard, especially during single player games.

There is a demo in development and it will be coming out soon. If I had to guess, I'd expect it to be out by the end of the month.