I didn't do the same buy-up, but I did a Trial Gold. I decided that Gold was the right level for me: lounge access for some int'l flights during the Trial period, a solid upgrade rate on my domestic flights, and good enough recognition by United when I have to fly them. I too felt that was the bigger jump up than Gold-Plat.
Case in point: I showed up to SFO a few weeks back for a nonstop United flight, my first on UA metal since the merger. Two pax, five bags, I figured my Mileage Plus Silver status was good enough for four of them and I was willing to pay $25 for the fifth. They were award seats, I already had E+ seat assignments, and I wasn't even thinking about my US status.
Much to my surprise, Silvers had their baggage allowance cut in half during the whole merger process.
Fortunately, I recalled that *G had a bigger allowance, so I gave the agent my US number. The allowance became 3 bags each, so all 5 were no problem. That Gold Trial saved me about $100 cash on the spot right there! (Figure with my UA Silver they would have hit me for $25 + $35 + 35 ??)