Hard to comment on efficiency (one of your tags) without knowing more context. \footrue and \foofalse are really each just a \let. So if the only reason that this token is let to one definition or another is so that you can decide whether or not to "do stuff" then you don't need the if token at all, then you don't need the test.

Just define 

\def\foofalse{\let\dostuff\realstuff}
\def\footrue{\let\dostuff\relax}


then you can replace the \iffoo construct with simply

 \dostuff


and it will either do nothing or the real definition depending on whether \foofalse or \footrue was most recently executed. Since this saves expanding \iffoo and skipping over the conditional text it is more efficient in principle but whether the difference is measurable on modern machines I haven't checked. It is unlikely that any of these make any real difference unless you do (literally) millions of tests.

Best practice for getting "If not foo" conditionals
In answer to this question, there was some discussion about whether these two sentences are equivalent:


  Art nurtures the soul.
  The arts nurture the soul.


Are they equivalent?  

'The arts' is a common but woolly term and 'art' is notoriously difficult to pin down.  Oxforddictionaries.com gives the following definitions:


  
  art [mass noun] the expression or application of human creative skill and imagination, typically in a visual form such as painting or sculpture, producing works to be appreciated primarily for their beauty or emotional power  
  (the arts) the various branches of creative activity, such as painting, music, literature, and dance
  


What practical differences in usage are there (if any)?

Also, does Art (capital A) have a special meaning distinct from art (lower case a)?  
