What margins do dealers who sell things like ATVs, snowmobiles, etc.
make? (New not used.) Are the margins higher or lower for the main
vehicles versus peripherals like ugraded tires, etc?

here's my free answer...  margins for peripherals are MUCH larger than
for the machines themselves.  using car dealers as an example, they
make gross margins of ~7% on new cars (on $20k ASP), 12-15% on used
cars (on $10k ASP), 45-55% on service & parts, and 100% when they
finance your purchase.  Likewise, retailers make little margin on an
iPod sale (5-15% gross), but huge margins on the accessories (50%+
gross).

the above stats come from publicly-traded auto dealers (AN, SAH, LAD,
etc.), I don't think there are any publicly-traded ATV/snowmobile
makers.  You can call local dealers to find the info, but of course
they do not have to answer your question...  You can also look at
Marine Max (ticker: HZO) as an analog in boats.  Polaris (PII) is a
publicly-traded ATM/snowmobile maker, but does not own its own
dealers.

Hope this helps.