I live in a relatively new housing development and the builder was kind enough to plant three trees in my yard. They range from 9-15 ft tall but they are all rather wimpy, each having a trunk diameter of a few inches.
Not having an entire lifetime for these to grow to full size naturally, I'd like to help them along. I'm considering plumbing several of those tree irrigation spikes into my irrigation system and watering the trees weekly for a TBD duration of time. That said, If I won't see much growth improvement, I'm not terribly interested in the hassle -- The trees are health, just not very big. Would these type of setup help speed up the tree growth?
No, not unless you're frequently in long drought periods which cause the tree to go short. The tree will grow as well and as fast as its genes allow with sufficient water for its needs, enough space for root development, and preferably good, rich soil to grow in. What's likely to be at question is whether the builder improved the soil prior to planting with plenty of well rotted organic material, such as composted manure, so it's probably worth mulching with it instead, but keep the trunk clear, don't let any mulch sit against it.
I tend to agree with @Bamboo. It might be good to gently do a little exploratory digging around the base of the trees to make sure the contractors removed the tree bags used to hold the root ball together. From what I've seen leaving the bags on (especially if they aren't just plain burlap) seems to be a death sentence for the tree. Another thing to remember is that it can take 3-5 year after planting for a tree to become established. At that point you're likely to start seeing better growth.