“hip” seems like a stretch to me, but comfortable and fairly interesting it is. Great location if you choose the address somewhat carefully. I think it is plenty walkable… but also generally think walking around late at night in most of the megalopolis is a bad idea.
From your post above and your participation on this blog compared to what I know about La Mesa and the people I know who live there, I think it would be great for you and your wife if you wanted a step down in intensity from the other three areas you mentioned.(Hillcrest, North Park and University heights). The larger lot, larger house for the money and somewhat slower pace seem like big pluses. I think the amenities/environment are pretty family friendly… if that matters. Lots less shock value opportunities. I sold a house on Mt. Helix recently to some friends. They are very happy with the reception to the neighborhood.I am sure you would be as well.
I have no strong opinion as to whether it will hold value or sprint up relative to other areas in the future. I think some properties in Clairemont might be better for that.That said, worst case scenario is probably relatively neutral.