There are many opinions here. Those with $ will recommend a 'might as well replace it while you're in there' approach, usually without regard to testing the component, just an 'on principle' thing since the engine may have lots of miles or is just 'old', or when you have to pay someone else to tear it down for reason A, so might as well take advantage of the labour $ spent and put in the parts that require the same time to get at them.
I don't think replacing the valve springs is worth the $, as I never heard of them failing or wearing out on the M116. On the other hand, if you have ticking at one or more cam lobes, this would be a good time to isolate the culprit(s) and replace the HLC(s) and maybe the rocker(s) and/or shims(s). You'll need to educate y'self on the procedures, all well documented on this forum.
Removing the valve covers is relatively minor work, but you should inspect the upper chain guides and tensioner/guide rail while you have the opportunity, and do a test to determine timing chain condition. See the DIY section for details.
With the right spring compressor, the valve stem seals are not especially hard to do, just a tedious job, and potentially frustrating if you're not very careful when removing the 'keepers'. While doing this, check the condition of the valve guides too. One worn guide and you're into head removal, I believe.

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1986 560SL
2002 Toyota Camry
1993 Lexus