Trademarks must be actively policed to remain valid. The C-D letter flurry is an unfortunate result but its the reality of how this particular type of intellectual property is managed. If there is any chance at all that you are infringing a trademark the holder is going to C-D letter you just to make sure they do not lose protected status for their marks in the future. The have to show due diligence at policing the marks if they ever have to go after someone who is deliberately infringing to hurt their business.
The one benefit of this approach is that there is really no such thing as a submarine trademark. Trademark owners are not allowed to sit on a trademark for a long period of time and then ambush others with a trademark violation in order to squeeze them for cash. I really wish patents had to be enforced like trademarks on most days..days ending in the letter 'y'.
The SparkFun example you bring up is actually an example of trademark policing working as well as anyone could expect. Trademark application filed... objection is filed...discussion happens...agreement reached. Does it suck that lawyers had to be involved. Yes. But that's the cost of doing business when working with any intellectual property issues.
Can you imagine if we had a patent system that was this efficient at making sure patent violations were brought forward on a timely basis as part of patent application filings.