I think there is potential in having a second chamber where the people making decisions serve a long term in office (possibly until they choose to retire) unless they are actively recalled. As you say, that puts them above the need to make decisions based on the worst kind of reactionary politics, as often happens to those serving for terms of only a few years who always have one eye on the re-election campaign fund.
On the other hand, I think getting into such office in the first place should be about more than buttering up the current PM. Rather like the US Supreme Court, if all you have to do to reach such high office is receive the assent of someone who may themselves be on the way out politically by the time they appoint you, there is a very real danger that too many bad apples get in and then can't readily be removed.
I've often mused idly over the jury service for politicians idea. For a while, I wondered what would happen if we ran a staged process where randomly selected citizens were invited to join the second chamber for one term of office, lasting quite a while (say 6 years), with a new intake every other year so you never have a chamber full of people who haven't figured out how things work yet. The difficulty I always run into is that like jury service, it probably has to be compulsory rather than an invitation if you're going to get a reasonably representative group, but unlike jury service it is clearly not reasonable to require people to give up several years of their lives for public service. And you can't really do it on shorter terms of say one year, because then the administration of the day can just wait out a hostile second chamber and hope for better luck next time before steamrollering through all the bad legislation it really wants in one favourable year.