I don't usually suggest FI cleaners,but instead using better gas. I have never run FI cleaner in my tC and I just hit 135k with no issues. I usually use QT regular gas, but sometimes run the higher octane for the cleaning benefits.
If I recall you bought this used,no?
Maybe the person used crap gas before, and a cleaner may help. Hard to say.
As for plugs.... They are 100k mile plugs, I can not believe that at 38k you have any kind of issue with those. I would hope that they were never replaced with cheapo plugs from the random auto parts store. Always, use the exact OEM plug for exact OEM performance. The only exception to this is if you have a major mod that requires a colder plug, such as BOOST or NO2.
If I were to suspect anything, I would be looking for any possible vac leak, torn or cracked intake boot, loose MAS, bad ground (most likely corroded terminal if this is it)
Best of luck