Intel Integrated Graphics are the bottom end no matter which version, though it's impoved over the HD3000.
Rolling back to 512 MB (in either the Mac Mini or iMac) could be painful after having a 1G graphic's in your MacBook Pro.
Plus the only way to get 1G graphic's in a new 27" iMac is in the 3.2GHz model.
If your photographic work is more than touching up with
basic noise, sharpen, etc. filters or your video is more
than just splicing and minimal enhancing you will probably
quite disapointed with any integrated graphics solutions.
As others stated, the HD4000 is quite an improvement over
the HD3000, it can still be outperformed by all but the lowest
end discrete graphics currently available.