I change my needles often. I stocked up in bulk from Allstitch so I always have a nice stock of them. And, yes, when the stitches start to go wonky or the tension "seems" off and affects the stitch quality it is always the needle for me. Worth the time to change it. oh, and yes, clean out the lint. That does cause the thread to bunch up,etc.
We pay big $$ for these machines..better to take care of them!
sandy