There would be no "New Deal" for Smith to oppose if FDR didn't run. People would judge him not by comparison to FDR but to Hoover--and he would therefore look pretty good.
That being said, I do not doubt that a Smith presidency would be more conservative than FDR's. (As I indicate at
https://www.alternatehistory.com/forum/threads/wi-al-smith-won-in-1928.451133/#post-17545720 I do not agree with people who say that "Smith moved to the right because he resented FDR as an usurper"--I think that in many ways Smith was a conservative all along.) I do not think this will fatally damage Smith's chances for re-election. There was a worldwide economic recovery from 1933-36, and it included countries governed by center-right parties--the National Government in the UK, the Lyons Government in Australia,
https://en.wikipedia.org/wiki/Lyons_Government etc. But at least one policy Smith advocated in 1932--a national sales tax--could have set back recovery.
I do not know whether the Democrats would in fact have nominated Smith in 1932 if he had sat out 1928. Obviously his chances would be better than in OTL's 1932 (when he had the burden of 1928's landslide loss) but the Democrats, sensing victory, might still prefer a less controversial (if only because not Catholic) candidate. In 1928 they were willing to take a chance on Smith because beating Hoover looked like a long shot anyway.