Doing repairs yourself are cheaper- but keep the LBS as backup for when thing do not go as planned. I am mechanically minded and only a few jobs on the bike I do not want to tackle so the LBS does them. But If I want advice the shop is always there.

And on upgrading--- I always use XT parts on my mountain bikes and that includes the Tandem that breaks parts just by looking at them. I do a hard ride each year and it is stripped to bare frame and rebuilt checking all parts as I go and replacing as necessary. I used to replace the RD every year but one year went up a grade to XTR. Following year and the XTR RD did not need replacing- Nor the next year. It lasted 3 years before I replaced it- but at the cost of XTR- I went back to XT.