The big problem with your rational is that prior to this season Zack Smith has never been a high percentage shooter over a full season. He posted an 18.2 in 2009-10 when he played just 15 games while notching 11 shots and scoring 2 goals. His previous career high overa full season was 10.4 and he got off just 136 shots that season. He's never even averaged 2 shots a game over a season where he's played more than 15 games either. Prior to this season, his career shooting percentage was sub 10%. So your assumption that he'll continue to do this is based largely on that at 28 he's now magically figured it out, and the 370 or so games that came before are completely outwieghed by his recent stretch to end 2015-16.
But let's compare him to another "garbage man." Tomas Holmstrom was one of the better ones. Managed a career shooting percentage of 16.3, so yeah, his was high. In his 15 season career he shot over 20% just 3 times, and in 2 of those seasons he managed just 74 shots in 73 and 67 games respectively, failing to hit the 20 goal mark in both cases. The one year he managed 30? He got a career high 176 shots on net (he never even hit 150 in any other season). And even prior to his first 20% shooting season, he had managed to shoot over 10% in each of his first 4 seasons. The only to 20+% seasons that came consecutively for him were in the 05-06 and 06-07 seasons, when offense was high due to the crackdown on penalties after the lockout. And to top it all off, he played on some legitimate powerhouse teams with the likes of Datsyuk and Zetterberg. I like our top 6, but no combination of Stone, Hoffman, Turris, Ryan, or Brassard comes close to matching Datsyuk and Zetterberg.
Point is, your comparison citing Smith as some quality "garbage man" really doesn't hold up. Andeven for the quality ones there tend to be sizable fluctuations in their shooting % and total shots from year to year.
Smith is a serviceable third liner. But to expect 20+ goals annually from here on is stretching it.