Like the good folks here have already said, you've got tons of options at 150.
What are you defining as an "upgrade"? Edge retention (kind of objective)? Materials and feel (much more subjective)?
The Stinger and Elementum you have actually have pretty good edge performance mated to a relatively thin BTE that really punch above what their pricing would suggest. Build quality on those is also quite good already.
The Endela in K390 (or anything K390) would likely yield the most noticeable difference in edge retention. Though, then of course, you'd want to invest in some sharpening tools. Only downside is K390 can patina and stain if that's an issue. In that case, the Manix LW in S110V would be the next best option for pure edge performance gain.
However, IMO, the build quality and feel would actually be lower than both the Elementum and Stinger with either the K390 Endela or S110V Manix LW. I personally like FRN; however there is a certain heft and touch that machined composites (G-10, micarta, CF, etc) have that FRN can't really replicate.
If the Spyderco Smock tickles your fancy, the 20CV version would be the one to look at. Only downside is that version is a dealer exclusive and it is currently out of stock.