I guarantee you there will be noticeable build up of carbon deposits around the butterfly valve even at 30K miles. Whether those deposits are decreasing performance is another issue; you'll likely first start to notice it in the idle. I did around 35K miles.
If you have the tools, you can clean them yourself. IIRC you'll need torx or allen wrenches for the TB bolts. Also, Walmart has a 3-pk of toothbrushes with stiff nylon, brass, and stainless steel bristles in the paint section that works great for me. That and a can of CRC Throttle Body Cleaner shouldn't run you much more than $10 and an hour or more of labor if you've never done it before. Still very easy
