The A100 is a good camera ... a bit dated, but still can turn out a nice shot.
When you speak of moving from it to an a700 or a550, you are proposing a threshold shift in what the camera can provide you with its enhanced capabilities, better noise response from a CMOS sensor, not a CCD.
Would it be a mistake? IMHO, only if you do not plan on growing your photography with a BETTER tool, because these cameras have almost everything you would want.
You mentioned you wanted "Live View." The a700 will not provide that. What the a700 has is functionality almost exactly like the a850/a900 Full Frame DSLRs. It comes with a wireless "Remote Commander", an optical shutter release and playback controller. The a700 also allows for "tethered" remote control, via USB, to your PC.
The a550 is not in the same class as the a700 ... and ramps down several of the more "advanced" functions of the a700. It does have "Live View" and depending on whether you purchase the a550 or the a500, there is a sensor size change and some speed abilities to decide upon.
Going forward, if you want "Live View" ... right now, the a550/a500 is your weapon of choice. If you want a true bargain for its capability ... a700 is a camera that will provide that, for a mere $850.
Tough choice. If it were me, the a700, as I have truly enjoyed that "tethered" feature.
a700 v. 04 w/ TAMRON SP AF 180mm f/3.5 Di LD MACRO
@ f/11 - 1/500 sec - ISO-1600 - Spot Metering - Spot focus - Cloudy - M - Tripod (RC)
It has gotten me closer to the "wild birds" than any other solution I have tried.
Hiding in the trees ... watching.
I would venture to say, there would have been
no way to get these particular shots with the
a5xx-series of cameras.
If you are interested in seeing more on this subject and its development, click on this link ->
Really REMOTE control