According to my math, 1-2 Japan trips and 2-3 transcon flights per year puts you somewhere in the range of 23,000 - 40,000 PQM's, and probably $1,400 - $2,500 PQD. If you're at the lower end of that range I'd either suck it up in Economy, buy an E+ subscription, or buy up to E+ per flight. The extra spend to make it to silver just doesn't make sense.

If you're at the upper end of the range I'd probably try to push for silver, either by booking into J for a couple of domestic flights (for extra PQD) or by upfaring where you can. If you're within $500 of the minimum spend, then you're probably at the level where it starts to make sense for you. Also in this situation I would try to do as much of your flying as possible on UA metal so that you're maximizing the benefits of silver. Since I had any kind of status on United I have tried as much as possible to stay on UA metal... Even though the service is better on ANA, the huge reduction in legroom compared to E+ on United makes it a miserable flight across the pacific.

If you have the ability to get the PQD waiver either through an international address or credit card waiver, then you might be close enough to push for gold, which is IMO a big step up in benefits

Hope this helps