I'd say there's really no point in downgrading to a Venture One. It earns at a lower rate than your Quicksilver. There would be basically no reason to ever use it. If you truly don't see using the card maybe consider closing it.
Ask for an annual fee waiver. If not, I would just close it. No point in PC'ing to a 1.25% card when there are many, many 1.5% and 2% cash back cards out there, also without the annual fee.
This might be too convoluted, but my suggestion would actually be to convert the Venture to another Quicksilver.
And then if it bothered you having two of the same card (it honestly probably would me), you could try to PC your current QS to the VentureOne.
Just in this case you would be getting the "better" rewards on the higher limit card.
Either way, I'd hate to throw away that $10K line and then they eventually start account combinations again. Or allowing Savor PC's again if that were more useful.
if you want to keep CL and account history, there is nothing wrong with PC to V1 then SD it.
Based on the responses, I will go ahead and cancel the card. I'm going to wait til my scores get into the 700s before I cancel tho. That way I can ask for a 15k limit on my QS without necessarily losing the 10k limit.
I'm not sure about what CLIs to expect, but waiting is good. It's a pretty good card for your current scores.
QS does out-earn V1. I'm not sure if V1 has some special perks that QS doesn't. It probably doesn't matter much, as your international spend will be limited (your current QS may be sufficient) and you have a DC earning 2% on domestic spend (albeit with a lower limit). I've heard the Venture "miles" balance converts to cash at 1 cpp, but others should verify that.
Someone afraid of planes may not want to bother with PreCheck or Global Entry....or maybe having it would make flying much less unpleasant. But that might be a reason to keep Venture a bit longer.
When your scores are higher, compare CSP to CSR. CSR requires a higher SL, but is often the better value.