I don't subscribe to the "start with a small refractor and then upgrade to bigger scopes over time" line.
Actually, I do (strongly) believe that starting out with a small refractor is probably the most effective way to get into the hobby. But I don't feel like it's an "upgrade" to a bigger scope. In fact, I'm currently working backwards. I've been imaging with an 8" SCT for many years now, and am "upgrading" to a 130mm refractor that will be my new primary imaging instrument.
Here is a history of imaging configurations that I've used (at least as much as I can remember):
Ultima 2000 mount with a wedge and an 8" SCT and Fastar (not Hyperstar, as it didn't exist yet).
Ultima 2000 mount with a wedge and an 8" SCT at F/10 and F/6.3. This was a horrible combination. Don't do it.
Celestron CGE with an 8" SCT at F/10 and F/6.3
Celestron CGE with an 80mm doublet refractor at F/7.5
Celestron CG-5 with an 80mm doublet refractor at F/7.5
Celestron CGE with an 8" SCT and Hyperstar
Celestron CGE with a 102mm doublet refractor at F/7.5 (the focuser on this one couldn't handle the load, so I didn't stick with it)
Celestron CGE with a 6" R/C
Astro-Physics AP1600 with an 8" SCT at F/10 and F/6.3
Astro-Physics AP1600 with a 14" SCT at F/11 and F/7
Astro-Physics AP1600 with an 80mm triplet refractor at F/6 and F/4.8
Astro-Physics AP1600 with an EdgeHD 8 at F/7
Astro-Physics AP1100 with and EdgeHD 8 at F/7
Astro-Physics AP1100 with an 80mm triplet refractor at F/6
Celestron AVX with an 80mm triplet refractor at F/6 (set up as an instructional rig to let people give imaging a try)
Astro-Physics AP1100 with an EdgeHD 8 at F/10
And my next configuration will be a 130mm refractor at F/6.3, and potentially with a Barlow at F/12.6 (or maybe a bit less extension). The AP1600 will be permanently set up at home, and the AP1100 will be the travel imaging mount.
The 130mm refractor is at the far end of premium, so I expect that it will beat totally beat the SCT for image quality, even at F/12.6 with a Barlow. The longer exposure times due to the slow focal ratio don't bother me. If this works out the way that I hope, the EdgeHD 8 will move from my primary imaging instrument, to a really nice grab-and-go visual scope (at least it's grab-and-go compared to the C14...)