The manual crowd and the machine crowd will each tell you their own stories. I have an orbital, I use an orbital. IMHO manual IS better overall. An orbital buffer can do a comparable job to manual but certainly not in tight areas. It is good for speeding up a job or giving your arms a rest. The only time I use mine is when I'm doing something that would really be a pain in the butt by hand.(de-swirling a friend's car for instance) Also if I have already done several cars in a row and my arms were gone.
Certain products work better, or should I say you can get better results using a buffer with some products and not with others. Example: Meguiars #9 swirl remover works great with an orbital and can be time/energy consuming manually. In my experience waxing does not seem to be helped in the least by the buffer. I always manually remove whatever I have just applied with a fresh 100% cotton terry. Bottom line; manual is the best, but the machine can help in certain ways and occasionally make things easier.
For vinyl and leather... For the plastic/vinyl/etc I would highly recommend Lexol's product "Vinyl-X". Either apply and leave on for the wet look or buff for a nice patina. Leather is more complicated. For a quick wipe down something called "Leather-New" works well. It is basically a liquid glycerine treatment. It smells like leather should and cleans conditions well enough for a one step process. For cleaning you can use either straight glycerine soap and a boar's hair brush or just a sponge and some Lexol leather cleaner will give you comparable cleaning results. To condition I would recommend Lexol leather conditioner. If you seek something a bit better and rarer I have some stuff for conditioning that will nearly revive "roadkill". It is called "Lederbalsam" and is made by Passier. This stuff is designed for ultra-high end equine tack but it gives unequaled results on any leather except suede. Hope this helps...Lee