Not entirely fair to Clark to blame him for Alonzo Gee's performance last year...
The amount of money thrown at Gee was minimal and it was for only two years. Some speculated he was going to get in the neighborhood of 4 yrs/$16M, and he ended up getting two years (guaranteed) and $6.5M. So if re-signing Gee was a mistake, it was a very minor one. Would you have preferred seeing Miles or Casspi playing more minutes at SF last year?
A good argument against Clark is that offensively he was most effective as a stretch 4. If I am not mistaken, it was when he started playing more SF, after Gasol returned to the lineup, that his shooting efficiency started to fall off (Pre All Star game: 47%/40% on 3s; post all star game: 40%/29% on 3s).
That said, he can defend the 3 and 4, and does provide some needed size to the team. We know how Mike Brown likes length on the perimeter. Even more to the point, Clark is actually interested in meeting with the Cavs. It's not as if the Cavs have their choice of FAs out there. Plus, if the Cavs sign him, it's safe to assume it will be on their terms, and won't impact their 2014 plans. This likely means a sizable one year contract or something similar.
Plus, Clark may be a backup plan in the event that some other SF option doesn't materialize. It has already been reported that Grant has been inquiring into the availability of veteran SFs.