Is it good practice to backport source packages from newer Ubuntu releases?

Question

My plan is like this:

Say I'm running 12.04 LTS, life is good, but its packages guadually become old. Then 12.10 is out, I add a deb-src line in my sources.list, and backport (download source, build, install) selected packages from the new release. Since the new release is supported, I should get security updates, on which case I will backport the updated versions. The system is still stable, and I get the new packages that I want, even with security updates (which I don't get if I go the Debian route and backport from testing).

Now the questions:

1. Is this plan as good as I think it is? I think it's the best I can get if I want maximum stability and security on the condition that I get these new packages I absolutely need. Right? Wrong?

2. If it's a good plan, how to do it in practice? In an ideal world, I think I should be able to just apt-get install something, and if the version with the highest priority comes from a deb line, install the package; if it comes from a deb-src line, download source, build, and install. But apparently the reality isn't so rosy, not only do I have to do extra work building and installing a source package, but I also cannot find a way to tell when there is a new version of the package from that repository! When I do apt-cache policy something, only the deb lines are listed. Why are source repositories discriminated against? How can I track a source repository and install upgrades as they come out?