I clean the bobbin area before I start a project. My machine came with a little brush just for that purpose. If the plate around the feed dogs pops off (check your manual to see if it does), clean underneath it. After doing 5 lap quilts you probably have little fabric fuzzies in there that look remarkably like the fabric from your quilts.
I don't worry about changing my needle unless my needle starts making "clicking" or "thwacking" noises. The "clicking" noise may mean your needle is slightly bent and hitting the feed dog plate. The "thwacking" noise is cause by a dull needle as it goes through fabric.
I also sew as well as quilt and will change a needle if I'm sewing fabric other than 100% cotton. Some fabrics work better with a particular type of needle.