Get Global Entry in lieu of SENTRI
SENTRI came first to the scene in the mid 1990's and has served it's purpose to ease travel between Mexico and the US, but IMO it's a relic of the past. For the general traveler, Global Entry is a better value as it serves all the functions of SENTRI and can be used at all pedestrian port of entries. Including Canada. If there's any advantages of SENTRI over Global Entry, I'm not aware of them. Not only that, but GE can be used at all major airports when returning from overseas and one can skip the sometimes ridiculous long lines to get through immigration. Oh, and for whatever reason, Global Entry is cheaper than SENTRI ($100 for GE vs $122.25 for SENTRI).
Border crossing & trolley etc
Visa will actually pay for a global entry application fee once every four years. I was really amazed to hear this. One downside to the trolley is that the last trolley leaves San Ysidro at 12:45 am. Street parking is not a issue. I always park on Border village drive.