Purchasing in Mira Mesa vs. Rancho Penasquitos should depend heavily on expected appreciation. On that score, MM ranks low for a number of reasons. The houses are old and need a lot of updating. The streets are crowded and full of parked cars and big trucks. The one and only poorly designed main drag, Mira Mesa Bl. is jam-packed and destined to get worse. Add now the possibility of mini-dorms as discussed here, and you have a neighborhood in decline.
Pay more for a RP neighborhood and you get a decent future. Hwy. 56 changed everything. Though it can get busy in a rush hour, it is generally 65 MPH. It is physically designed to take a third lane in each direction, so that will eventually happen, as is happening to 52.
