You make some good observations on mid-caps in Vanguard's small cap value fund, plus you're aware of low expense ratios and have diversified well. But I see a 0% bond allocation, which will need to change before retirement (to reduce risk).
I've read numerous books by Larry Swedroe, who favors a small cap value tilt. But one of his more recent books on "factor investing" has some new ideas that might be worth considering. Actually, some are quasi-new ideas. For decades Warren Buffet has been beating the S&P 500 (but more recently is probably tied), and academics didn't really know what he did differently. But two of the new factors (quality and ... another factor I forgot) explain Buffet's performance. In other words, you can invest in a fund that tilts to those two factors to try and target Buffet's performance - and on smaller companies than Buffet is able to buy (since they don't move the needle for the billions he has to invest).
So keep the small value + small cap tilt, or consider new factors.