Iridium spark plugs for M30 engine?

I recently started "tuning up" my cars. For my 2000 Toyota Sienna minivan, I put in Denso Iridium plugs. Wow, very nice. The engine responded to it
immediately and feels very lively.
For my 1990 535i, 5 spd, 128k, I put in some NGK ZGR5A standard plugs. Car ran well, but definitely didn't have that "lively," "responsive" feel I got when I put iridiums into the van.
Has anyone tried iridium plugs in a M30 3.5l engine? If so, what did you think, was it worth it? Or should I just be happy my car still runs....:) Thanks!
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