This can have negative effects on technique. Especially for dynamics. Trying to play palm muting, quiet finger passages over the bridge pickup, etc without any amplification are very difficult to hear. Even with a resonant, chambered electric bass with brand new round wounds (which describes my main bass). OP mentioned playing blues as well, a lot of which is played with a lighter touch. This has been my experience anyways. Practicing scales and such unplugged while having the TV on was a regular occurrence for me at one point. When I would play with the same force through phones or an amp, I found I started to become pretty ham-fisted with my plucking hand.
I actually find it is the opposite for me.
I practice about 99% of the time unplugged, and have done this for the last 20 years. By doing so my touch, technique and dynamics have improved immensely. If it's just you and the instrument, every bit of unwanted noise is you and there isn't anything there to mask it (like amp eq) so to fix it you need reassess your actual techniques and make adjustments until you can cleanly execute whichever line you are playing. I find that if you end up sounding a lot better amplified too because if you clean up your sound from the source (string manipulation) everything else follows.
When you do plug in during rehearsals and gigs you are not relying on the gear to do anything except for making you louder, or tuning the bass response of particularly horrible spaces.
It's not just dynamics that improve but also tone as you learn to make the notes sound brighter or rounder by playing at different parts of the string and experimenting with varying levels of muting. Basically if you can get to the point where you are producing the desired tone directly from the strings themselves then you simply amplify that tone.
I think people should work on sound production from the source, just like singers, horn players, acoustic string instruments.
As for not being able to hear it, now that is definitely something I cannot relate to but then again I don't have other noise sources like a TV going when I am practicing, I focus on practicing. If I do need to listen to a particular tune to learn it, I don't have it so loud I can't hear the bass and as soon as I have learnt the tune I internalize the feel and reproduce it without the "backing track".
I only needed to " play along " with song in the early stages of playing, the first couple of years. Since then I feel that if I can't reproduce the feel of a particular tune by myself unamplified then I haven't learnt the tune well enough
Of course we all have different perspectives, this is just what I've found works for me.