If you're looking for a meeting place or a good stop around ½ or halfway between Alpine and Vista, you can try The Woods Trailer Park, CA, which is about half an hour west of Alpine, or about half an hour south of Vista.
About ⅓ or a third of the way, you can stop at Santee, CA. This is about 19 minutes west of Alpine.
About ⅔ or two thirds of the way, you can stop at Rancho Bernardo, CA. This is almost an hour northwest of Alpine, or about half an hour southeast of Vista.
About ¾ or three fourths of the way, you can stop at Escondido, CA. This is almost an hour northwest of Alpine, or about 15 minutes southeast of Vista.
If you drive straight through without stopping at all, the total distance is 58 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 1 hour, 1 minute.