My son adores Legos, and yes, this does bother me. So, here's how we have hacked the problem:
First, I bought his first Lego "sets" at consignment shops. Lots of mixed pieces, no directions, not expensive, just ziplocks or shoe boxes of random bricks from Goodwill, second-hand stores and garage sales. He had these long before he got an actual 'set'.
Then, when he did get sets, we used those to build that one item, but integrated the pieces into our other collections. I offered other purposes for the Legos; one of our favorite things we did was to get a board and build 'enclosures' for his little Hex bug nano, complete with pieces that spun and doors or gates which could be opened and closed to direct where the bug could go. Yep, I'm kinda geeky like that.
Now, we are using the instruction books as reference guides. Our current project (he likes to work with either my husband or I on larger projects) is a "Dark Fortress", with trapdoors and hidden closets. If we don't remember how to construct an element, we refer to the guides or to the Lego Idea book. YouTube also has a wealth of basic how-to information... we like seeing the real and Lego trebuchets and catapults. Future projects!
Honestly, at first I was disappointed that everything came so proscribed: this is how you build it, exactly. What I have noticed, though, is that my son has really gained confidence in following the no-words directions. This has also helped him to better understand step-by-step drawing guides, which is something he's really into right now. He uses them as I often use a recipe-- a loose framework to integrate our own ideas into. For younger kids, this is a sort of entry point for later work such as following recipes, step-by-step instructions for constructing a model or maybe woodworking when the kid is older, or even following patterns and sewing one's own creation. When kids gain this sense of mastery of knowing the basic elements for building a desired item, then they can begin doing it on their own, making tweaks, changing the original idea to suit them. So, I'm valuing both my son's imagination as well as his potential to keep finding those little blocks interesting because he feels he can make anything he wants.
Interesting post topic-- thanks for making me really think about this!