Interesting rendition Emanuele. If you were running a 3nm Ha filter with a red continuum filter, I'd say its plausible...but there's only so far you can take the dust&scratch or clone tools in PS.
Narrow fields are the best for starless scenes. Wide fields just look plain wrong IMO.
Sounds like you're doing something wrong in MaximDL if you're not hitting focus. I'm assuming you're doing the task manually...Once you've cropped a star that you intend focusing on, within the camera control dialogue box, click on the inspect tab. Monitor the FWHM or HFD values as you work the focuser in and out. You should be able to reach focus without too much pain. Just don't select a bright saturated star as the readings are likely to be erroneous.