To be honest, I really don't know, nor have I ever heard, of any long term degradation of the engine while using the Smarty Jr. The "JR" does not make a rocket sled out of your truck so, with that in mind, 'my guess' is that any excessive wear would not be that much.
I have a "JR" on my '03 & love it. I tow on the TOWING mode & it does a good job. Otherwise, I drive on the PERFORMANCE mode. I, occasionally, do 'hotrod it' just for fun. It provides more than enough power, for me.
I don't beleive the "JR" has been out long enough to show any long-term issues with its use. Also, how long do you anticipate keeping your truck. If only a couple of hundred thousand miles or less, I wouldn't worry, at all. My guess is that the engine will last MUCH longer than that even with the "JR's" use. Like you said, if you don't "abuse it", just enjoy it.
Joe F.