This note is not mine, but one that Dan Milway sent me (here). He blogged about instrumentalism as the guiding philo of science position in linguistics and argues that adopting it fervently is misguided. I agree. I would actually go farther and question whether instrumentalism is ever a reasonable position to hold. I tend to be realist in my scientific convictions thinking that my theories aim to describe real natural objects and that the aim of data collection is to illuminate the structure of these real objects. I think that this is the default view in physics and IMO what's good enough for physicists is good enough for me (when I can aim that high) so it is my default view in ling.
Dan's view is more nuanced and I believe you will enjoy reacting to it (or not).