For through-the-scope deep-space astro photos, the ETX line is not suitable. The mount is simply not made for photography, and the long focal ratio makes exposure times unrealistic. I own an ETX-90 myself, as well as a 10-inch LX200GPS, a 12.5-inch Dob, and an 80mm semi-apo refractor. The ETX line can be used for through-the-lens snapshots of the Moon and planets. It can also be used quite well for piggybacking a 35mm camera for long exposures, using lenses in the 20-to-135mm range. (A typical 35mm camera lens is 50mm.)
Don't worry about the "low contrast" for planetary observing of an 8-inch SCT. An 8-inch SCT will match a 5-inch apochromatic refractor for planetary resolution, if both are perfectly made--this statement has been published repeatedly in Sky & Telescope. The supposed loss in contrast from the central obstruction is offset by the increased resolution and light grasp of the larger scope.
For proof, look at the pictures of Jupiter in Sky & Telescope or Astronomy. They are nearly all made with Meade or Celestron Schmidt-Cassegrains. Those scopes now make the best groung-based, visible-light photos ever made of planets, including images by professional observatories (though adaptive optics will some day give the observatories an edge, as is already the case in infrared). Plus, with the SCT, you can get the f/6.3 focal reducer and a billion other accessories.
Go for the 8-inch SCT. The only drawback I see to it is that a German equatorial mount is harder to transport and set up than a fork mount. If you have enough cash left over and have a garage where you can leave the scope set up, Wheely Bars from JMI will allow you to be viewing within 5 minutes.