Six owners is a bit many, but many Porsche's are third or fourth cars and tend to be bought and sold on a whim rather than need. Its very common for any used Porsche to have 2-4 owners.
The lack of service records alone shouldn't be a deal breaker. Lots of well maintained cars don't have service records. A well maintained car in great condition with service records will get top dollar whereas a car in great condition without service records will be slightly less valuable. Adjust your price offer accordingly.
To mitigate the missing service records, most new owners in this situation assume that the last significant service was not done and they take that amount off of the asking price. For example, you would assume that the 30K service wasn't done and take that cost off the price and then have it done as soon as you buy the car. This gives you some peace of mind and a clear starting point on maintanence. Just call a few local shops and ask for the price of a 30K service to find the amount.
The most important thing to do is to get a Pre-Purchase Inspection at a local Porsche shop or a dealer. I know its a pain in the rear to arrange and execute but take the time and do it anyway. This can save you thousands of dollars! The shop will know what to look for as they check the car over end-to-end. This will give you a good idea about the mechanical condition of the car and what repairs are needed. Be sure that the PPI includes reading the engine computer to see if any fault codes are stored (which might be there even if the Check Engine Light (CEL) isn't on). Expect to pay $150-$300 for this service. This is the best investment you can make so you know what you're getting into.
As you may have read, there are no cheap Porsche's. Repairs and parts can be somewhat costlly depending on where you're coming from. Rememeber you're buying an 8-yr old car so plan to have some money in reserve when you buy it. $1,500-$2,000 should be sufficient. Oil changes are $100, new tires will run $700-$900, a new starter is $400 DIY or $750 at a shop, etc. You get the idea. Its not abnormal to spend $1,500 in the first year of ownership to get the maintenance caught up and fix a few things that need fixing.
On the plus side, if you buy a Boxster you'll completely fall in love with the car and have a smile on your face every time you drive it.