1) Side x Side Twin homes are tough sells and very challenging on resale. Most of the time people buy these because they want to live on one side and rent out the other. The only other purpose is a buyer would like to buy a single family home but the neighborhood is expensive, so they buy one side of a twin home. In up markets it is easier to sell, but they do not appreciate very well due to being valued more often than not by rental income and not single family appreciation.
2) In Blaine the prices are not high enough, and there are quite a bit of really nice TH associations like Club West. TH side x side are incredibly cheap right now and will appreciate more in the long run. They also serve a very niche purpose versus twin homes, and this makes it easier on the resale side. There are a lot of buyers out there that don't want the maintenance headache. Certainly End Units have a slight advantage, but so does beds/bath count (huge impact on resale), and the positioning of the UNIT (does your view look straight at another Unit or no?). Floor Plans also have an impact, so all of these factors come into play and a Realtor can help discuss this further.
3) Single Family homes will always appreciate much more than TH's as a general rule. In Blaine I can either get a decent TH for $130,000 or pay just a fraction more to get a decent Split level home. The Split level home should appreciate more in the long run.
4) Location will never change throughout the history of Real Estate. School Districts, low crime rates, & amenities today's homeowner is looking for all come into play.
That should hopefully give you an idea, and of course feel free to contact me directly on Trulia if you have any specific questions since I know Blaine and the surrounding areas very well. Part of being a Realtor is understanding neighborhoods and this question very well. Real Estate is hyper local so in the end the best way to answer this question is be property specific.