You lose redemption options, not value. They remain UR points. If you don’t spend them, you can transfer them to one of Chase’s premium cards at a future date and make use of the better redemption options. OP indicated a Southwest preference, op might transfer some points out to Southwest (if remaining) at the end of the year.
Sw points are usually worth slightly under 1.5c/$ after the most recent devaluation this year. SW points ARE more flexible for cancellations, but I’d hesitate to transfer many extra points early from UR due to SW’s history of ~annual devaluations.
On the travel portal topic, I’ve only used it for non Southwest flights myself. Airline prices in the travel portal tend to match public prices. IME Cars have been more expensive or poorer providers than through Costco portal. Hotels have been more expensive (for like cancellation terms) and lose status benefits vs booking direct. I am mainly comparing with Hilton’s though, which usually have between 12-36hr notice required for penalty free cancellation and 20%+ value in rewards earned when you pay with money booking directly.
That brings up a second credit card suggestion I have to consider. A good card on an ongoing basis until they cut benefits. Amex Hilton Aspire. $450 annual fee. Opening reward:100k points (worth ~$400 at lower end properties or a little more at an expensive one) plus one weekend night at almost any Hilton. Yearly benefits: $250 airline fee reimbursement (works on Southwest giftcards, at least as of last I checked), $250 refund from a Hilton “resort” stay - most Hilton or higher places, must show up on a website portal they have, Hilton Diamond Status, and a free Weekend night (no spending requirements). I received a credit for a hampton inn stay only after calling in because I didn’t realize it was only a limited list and the portal they point you to has an entry field where All Hilton properties will show up. So it technically was on the page they linked to.
The one night stay is worth $100 even at a low end place. Airline reimbursement currently works for GC, so worth around $225. Plus a refund of $250 from a Hilton stay that I’d value at $225. So, on an ongoing basis you get $550-$750 and you also get Hilton Diamond status if you value that at anything, which exceeds the annual fee. I have had good experiences at Hilton Garden Inns in the past, and I place a value on the Diamond only (partial for Gold) free breakfasts. Whereas I place no value on the “included with all rooms” Continental breakfasts at Hampton Inn or similar.