Using on page SEO for local results can still appear in the main searches nationally if your page is strong enough. So using SEO for local purposes should not effect your national rankings at all unless you are using lots of on page SEO such as Page Dilution.
Page Title: The Name of the Product | Bournemouth for Example
Meta Description: Description of the product including the keywords of
Page Content: Again about the product and over use of the word
Using the above as an example this can dilute the page a bit while not making it impossible to rank it does make it harder.
Things that can help you rank Locally and Nationally
Please note that these are not Google Facts but generally what SEO'ers believe currently. Google is pretty good at keeping secrets.
Targeting Local People
When targeting locally for example in the UK and using Bournemouth as an example your also targeting Dorset and the Country UK. But to appear in Dorset or UK there's more competition since more sites are all of the 3.
Schema is GREAT! but its only one factor of many
Using Schema is great and of course you should be using it but you need to know it's not just about the Data that your providing Google via on PAGE SEO.
Most Local Rankings is off page SEO.
Most Local Rankings is actually done of the PAGE SEO and there is many ways you can establish better local rankings as well as national. These includes activities such as:
- Citation Building
I've found this to be one of the most beneficial mentions in ranking sites for first page and top rankings. Citations are basically having sites have details about your company. The key element here is your company name and address Google uses this to confirm that your company is who it says it is and most important located where you say it is. The more you have the better, and there are different types that can help as many believe that some pass more citation than others. Good sites in the UK for example are Yell, BT, Scoot etc. But some citations on local sites in your area works really well too and these are golden. It's important to note that you don't need a backlink for a citation to work - Just ensure that your company details are the same on all sites as this could confuse Google.
- Local Back links
Having back links is a great thing but some local ones help too since if they in the same area its kinda like saying ok we trust you more, sure this is unproven but many claim this to be and I'm one of them.
- Google Plus and Google Places
Google Plus and Google places is an absolutely must not only do you confirm the address which is a key element and one that I consider the most important, people can leave you reviews and this is another key element while its hard to say much a review helps it does help some what but also improves your click rates too which ultimately is what you want and the more clicks the more chance of sales and natural back links occurring.
- Bing also has a Places type thingie ma dingie!
While Google is an example factor don't forget that most machines come with Bing as default as the search engine so many still use that, submit to http://www.bing.com/local/uk/
- Reviews on other sites other than Google.
Doing reviews on other sites is worth mentioning too, while no one really knows how much they help it does pass trust and especially if people see those reviews. Try to get as many legit reviews as possible. Rather than sending out emails and emails to customers in one go you should do a competition or something like that and send them out in batches.
- Take a look at your competitors Citations
I recently used a Citation finder that compares what other people are using in the same field, take a look at http://www.whitespark.ca/local-citation-finder/ and they are really good. I only needed one month so its pretty cheap.
- But what about National Rankings
This is pretty much the same old thing, build good content and hope that people back-link because your a GOOD company and your pages often more than others. There is billions of sites that can be easily found to help on this area so I won't list every SEO factor here.
But to answer your question in short as long as your not adding the area within the PRODUCT Schema, then you should be fine.
But no your local rankings should not be a factor as long as your not entering local data into the Product element. Use Citations for local rankings and so on.