I think it's easy to "stock" the SS position with a cheap plus defender, but we'd lose a lot on offense in an era where offense is exploding and the SS position is becoming a much better offensive position than when I first started following baseball.
I actually don't think Bogey is "fine" on defense and never did. I thought I saw some growth on defense a couple years back, but it seems he's leveled off. Some numbers even show regression.
I'd love to have a top defensive SS on this team. To me, it doesn't matter, if he can hit real well at all, but if he wasn't "black hole" I'd be very happy. Right now, I don't see that guy in our system. We went a long time before Bogey trying to find a SS who could give us stability for a long period. Bogey's okay on D, but he's been a pretty big plus on offense, when compared to other SSs. On an offense trying to adjust to the loss of Bogey, I'm not sure we are at the time to consider intentionally downgrading our offense at any position.
In an off year, Bogey is still the 9th best offensive SS in MLB (fangraphs) and is tied for 8th in SS WAR. Last year, he was 6th in SS WAR and 4th in Offense at SS. He was 2nd in WAR in 2015 and was the best offesnive SS in MLB.
I don't think Bogey is just incrementally better than the average SS in MLB. I hope his 1.5 year decline is not a thing to expect to continue, but it is worrisome, especially the no defensive growth part.
2015-2017 SS WAR (34 with 1000+ PAs)
14.0 Lindor
13.9 Seager
12.2 Correa
11.2 Crawford
11.2 Bogey
10.9 Simmons
#10 Segura 7.3
#15 Semien5.1
#20 Flores 3.4
#25 Miller 2.7
#30 A Escobar 1.4
Bogey has been 4th in SS offense at 30.4, and then there is a big drop off to #5 Nunez (18.8). The 17th SS (mean) is Simmons at -4.4. That's a huge loss in comparative SS offense, if we were to trade Bogey.
Now, some of these numbers are cumulative in nature, so here's some other SS data from 2015-2017 (34 SSs with 1000+ PAs)
Bogey ranks...
3rd in OBP at .351 (the mean is .317.)
11th in SLG at .427 (just above the mean of .413)
5th in OPS at .778 (The mean is .728)
7th wRC+ at 107 (The mean is 97)
FYI
Bogey places at #17 in UZR/150 at -1.3 during the same time period. (41 player sample size: SSs with 1000+ innings)
In short, I would not overpay to keep Bogey here like I would for Betts, Sale and JBJ, but i wouldn't look to trade him this winter just so we could afford a better 1Bman.