Be careful, sometimes canned air can force dust even further into your machine. I would also worry about something besides air going into my machine.
I never let my machines get that way. I clean them every time I change the bobbin. I keep canned air handy and just blow out through all the openings and above the needle area. Works like a charm. IMHO, with prices the way they are these days our machines are an investment and need to be treated as such."