My success with seedling selection has been most notable with rambutan. I have a selection we call "Singapur" that compares well with the Asian selections that have been introduced. I also have one we call "mora" that is very large, stone free, and a tad tart but with lots of flavor resembling blackberry. I have a pulusan selection as well.
What prompted my earlier comment is that I have worked with hybridizing bromeliads and anthuriums. In most cases you don't want natural pollination when making crosses but interesting surprises can occur. Natural pollinators show up who are more aware of when the flower is receptive. In my case in CR a wild plant could inadvertently cause a surprise cross that nobody had been able to do before.
Anyway, for people who have the space and time it CAN be rewarding to plant out seedlings and even if the desired cross was not made you could possibly get a valuable plant.
Peter