It's not a problem, it's just a little bit of a wasted effort. First, EMD's have less of an impact as they once had - so rather than trying to game the SERP's with the micro-sites - you can just kill it with local content on things to do once you rent the car. Think of these other sites as opportunities to create an umbrella of related terms to your main keywords - with links back to your money site.
Also would 100% differentiate the layouts for each site - the more unique each site - the more value your links will have within your network of websites.