The addition of boxes and such, while nice, won't push up the price appreciably, because this Pentax camera and lenses are not collectible items.
The body most certainly will need new foam seals. I am not a fan of using the word "mint" to describe cameras. It has become a deceptive word because of how eBay sellers use it to describe anything that appears to be working. The use of this word now seems to apply to anything that doesn't have a mark on the exterior, which is inaccurate.
The body probably would bring maybe $50-$75. Is the owner's manual included? And is the manual in good condition and not with the owner's name or notes scribbled inside? For this camera, the owner's manual is more important than the box.
The 50mm lens is fairly common. I would guess about $20-$45.
The 28mm lens might bring $25-$50.
The 135mm lens is the gem of the bunch. Most 135mm lenses are of the f/3.5 variety. The f/2.5 version should increase its value to somewhere around $100-$150 from the usual $40-$75 for the f/3.5 version.
The filters add some value to the kit, depending on which filters they are. Polarizers and some filters for b/w should bring more than color-correcting filters for shooting under incandescent lighting.
Your estimate sounds about right -- give or take $25-$50. It sounds like a nice kit.