Is it necessary to replace the spark plug boots when replacing the spark plugs? Rockauto recommended doing this when I went to order some spark plugs. And are the NGK ruthenium spark plugs any better than they're iridium plugs. Not much more cost, but I don't know of anyone that has tried the ruthenium to give me a real world experience.

 

They like to recommend parts for 2 reasons, to boost sales and also what tends to ne missed when doing some services.
Yes boots should be replaced if you have more than 7-10 years or over 100k miles. The rubber does start to deteriorate even if you can see it and will allow for spark energy to go through them. Generally, it will generate a DTC misfire code that tends to be tricky to find why it was generated. Visually looking at them if they are dirty, oily, cracking at any area. or tend to have a shape formed from being in a location for a long time you should spend the 3-4 bucks each and just replace them.
If you have access to an oscilloscope, then you can actually see if spark energy is being used and losses because of poor boot quality.

Don't forget whatever you decide to use dielectric grease alone the inside edge when re-installing them back on the spark plug.