Boxing is a staple aspect of MMA for very good reasons. If you have a chance to take it up, I would do it. Here's a few things that you can get from solid boxing training:
1) Boxing helps in developing effecient, powerful and accurate punches. Let's face it: Your hands are the most used striking weapons in combat. The funny thing about all of that is that most people don't know how to punch correctly, or in an effecient way that won't make them open for shots. Strict boxing work goes a far way in improving that.
2) Boxing helps develope solid punch defenses. Like I stated above, the hands/fists are the most commonly used striking weapons in a fight. The best part of boxing (in my view-as I've state many times before) isn't learning how to punch; rather it's learning how not to get punched in the head.
3) Boxing provides solid cardio/conditioning training. If you find a place that is even moderately serious when training, you're going to push your conditioning every time you step for a session. Combine drills, with calesthenics, with bag work, with sparring, and everything else and you end up with a great workout.
4) Boxing will provide you with live sparring. You mentioned that there is no sparring where you currently train, and I think that's unfortunate. I view the greatest downfall in most places that teach the "Traditional Martial Arts" is their lack of sparring. Truth be told, you can do forms, drills and all else, but if you don't spar to find out what works or how to apply the things you've drilled in a live situation, it's going to be detrimental to actually put those things to use. I don't know of any moderately serious boxing gyms that don't do sparring of any type (provided there are enough people training). Just make sure you get a hold of the appropriate equipment and you'll do fine.
Now will it completely destroy your concept of fighting/combat? No, not if you keep your training in perspective. If you keep things in perspective as to what works for boxing, what works for MT/Kickboxing, and what works for MMA (as that's what you're wanting to progress to) then you shouldn't find yourself "disenchanted" or jaded over the time you've already dedicated to training.
Hope that helps.
It doesn't matter if you agree or disagree
... As long as I don't bore you and I spark a moment of thought, my goal is achieved
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