Although the intent isn’t that spammy, sending an email may make it look that way and it’s likely you will be ignored.
(Not always though — see this example of an agency that contacted Rush to suggest they needed a new web site: http://www.plankdesign.com/blog/2014/12/plank-happy-cog-working-rush/)
Dropping by in person could have a completely different outcome, as long as you come up with very strong reasons why they should have a better web site, and come up with solid arguments how a new web site will bring in more business. A face-to-face chat is already good proof that you care enough about their online presence.
Keep in mind though, lots of local business simply don’t care. As long as they have a web site, they’re happy, and they don’t need anything “fancy” (to them, having a site in itself is already fancy enough).
And, of course, a lot of businesses think a web site costs $300 at the most. ;)