It's hard to PC QS1s. I was able to PC two of them after 12 or 13 consecutive months of usage and payments. We don't have enough data points to know that there was a connection between usage and the PC offers or if it was just a coincidence. But definitely call in each and every month while you still have the card to see if an offer has appeared.
I wouldn't grab the Platinum because with a Venture and a Discover, your profile is beyond that. I like the idea of grabbing a new card and combining the QS1 into the Venture, though. You could grab a Quicksilver or a Savor. But I think my preference would be to add a card from a new bank.
Note that Capital One requires a six month wait between new cards, so that might come into play. If you're looking at a card from another bank, you'll want your timing to be right. The bottom line, however, is that it's beneficial to have three open cards, meaning that I'd have the new card in hand before losing the QS1. If it means eating one more annual fee to do this right, it's a small price to pay.
