Is it a terrible idea to aim for a lower journal for a paper?
From my point of view, there is nothing wrong per se with submitting to a low-tier, non-spam journal. I have always maintained the position that if you find out mid-way that your work isn't what you want / should be doing, it's better to submit what you have to whatever is achievable at this point than to either stick it out or throw the work away entirely.

However, in your case it actually sounds like you may want to go for another iteration at the mid-tier anyway, because you don't think your work is that bad, it's just the write-up - and this can be fixed with a modicum of effort, in the worst case re-writing the paper. Also, assuming you are an early-stage researcher, getting more writing practice is basically never wasted effort. In the end, we are not talking about investing a year more into this project - it's a few more weeks for re-writing, and then some on-and-off effort for revisions. Finally, would it not be annoying to you to "waste" your work to a low-class venue just because you did not want to write it down properly?