I've carried my Ace [250 now 400] in my truck all year except DEC to MARCH when its too cold to detect.
Never had any problems and if it get stolen, oh well. I also have a nice GPS, radar detector, dashcam, battery booster, stereo, sub woofer, top of the line power amps in my truck, all of which would likely get stolen before my Ace.
That said, I wouldn't lug around my Deus all year, I'd cry if that got stolen.
I look at it this way - I have found many many things just because I happened to have a detector with me and felt an impulse to pull over and go detecting. Would not have found half the things I have found or discovered the hot spots without having a detector handy at all times.
If heat is bad for a detector, mine never got the memo.