If all you are using the keg for is dispensing, and the keg is not sitting somewhere room temp for a while in-between filling, what you are doing will most likely not impact you negatively. Leaving the keg with only a rinse style cleaning at room temperature is asking for bacterial growth.
The poppets in the posts tend to build up gunk in the springs that can be difficult to clean simply by the beer sitting on them. The o-rings, poppets, and pressure relief valve will get some beer under/between them and you cannot guarantee that proper cleaning or sanitation occurred. You should also use a brush to clean the dip tube. I would not consider a keg that was not fully disassembled to be sanitized. Therefore, if you are also using your kegs as secondaries, I'd make sure to disassemble them when cleaning and sanitizing.
Your dispensing equipment should ALWAYS be cleaned via disassembly and brush, especially because of the plastic bits. There is no way to assure a proper cleaning without doing this. I'm sure you have been to bars where the tap beers, especially the rotating ones, have an off-taste - this is because they do not properly clean and brush the dispensing equipment when they change to a different keg.
I'd also suggest replacing the o-rings when you do disassemble them. Folks have a tendency to overtighten the posts, pinching them, thus making the o-rings unreusable. The lid o-rings, unless pinched by not paying attention, rarely need replaced. The o-rings, purchased in bulk, are quite inexpensive from an industrial supplier like McMaster:
DipTube: ID 5/16", OD 1/2" (AS568A Dash Number 109) McMaster 9452K172 Buna-N $2.21 per 100.
Post: ID 7/16", OD 5/8" (AS568A Dash Number 111) McMaster 9452K23 Buna-N $2.48 per 100.
Lid: ID 3 1/2", OD 4" (AS568A Dash Number 417) McMaster 9452K218 Buna-N $12.69 per 10.
If you have a restaurant supply store in your area, I'd suggest getting a food grade silicone spray or squeeze tube - it doesn't take much of either to make a good seal and is generally cheaper than at the online stores when you figure shipping in. You should re-lube every time you loosen a fitting with an o-ring.