I am proud to take my Singer 301 to any group/class. So far nobody has criticized it and many have admired it. If people are making suggestions about thread and other things, I would recommend asking the teacher as long as you are finding her attitude to be positive and you respect her opinion.
To me, sewing machines are like our bodies -- if we have used them for years, we know them better than doctors and quilting experts. That doesn't mean that we don't seek advice from professionals (and sometimes from friends), but we consider it along with our own first hand evidence before doing anything drastic.