Tried that intuitively in the first place... to no avail I fear
Reinstalled FS2 in a different directory only to uninstall it again hoping thus the regentry would be wiped -> unsuccessful
used CCleaner to clear registry after uninstalling each FSO (mod) or FS2 copy -> unsuccessful
*Of course each step followed a new installation of diaspora
@Matth
I feel thanks are in order for making efforts to help me in lightning speed

Just for the record: the smeary effect that affected both backround texture and objects was related to emperimenting with graphics settings namely enabling post processing. I have a HD 6950 ATI GPU
Problem solved!
run as administrator seems to override user related settings