I voted Yes but with caution...
As far as spyware is concerned, avast detects the most dangerous ones... If the antispyware thing integrated into avast will be something good... It will appeal to a wide range of people, so more avast users...
However, it is best if the adware definitions are bundled with the virus definitions and the adware detection will be integrated within the standard shield process... This way i believe the computer performance will not be affected... But keep in mind that alwil will have to cope with something new that is not so familiar with... I mean there are, how many, 17 years of happy virus detection...
let alwil do what thinks its best
As for the registry, I would vote a No... Because, is it really necessary? Again, it is something that doesn't have direct connection with viruses...