When it comes to Mo, I'm pretty agnostic.  I wouldn't give him away as a throw in in a trade, but I also wouldn't hesitate to trade him if we get value back in return.
The pros: he's an average, to slightly below average, starting SF who is only 24 and on a reasonable contract.  He doesn't suck on either side of the ball.  He's pretty much average at both offense and defense, which makes him the closest thing we have to a 2-way player at the SF spot.
The cons: he's been in the league for five seasons, has started over the half the games he's played, but hasn't really improved much since his rookie year.  The only improvement of note was his 3-point shooting last season.  He shot just below the league average 3FG%, but only made 68 3-pointers.  That's not a huge sample size and I'm not sure it's sustainable.  Remember - Aminu made a similar jump in 3FG% the previous year, but on a much larger sample size (126 made 3-pointers) and then backslid last season.
I guess I just don't see where this untapped upside is.  He hasn't been lacking for opportunities, either in ORL or POR.  He has been a starter and played plenty of minutes in both places, but has never made any big leap forward in his play.  At only 24, there could be some continued minor improvement, but I just don't see that he has the tools, or the attitude to become an above average 2-way starter.
Which is what I really want at both forward spots - players who are above average on both sides of the ball.  And, if we can get one of those I'd gladly move Harkless.  Although average as a starter, he's worse coming off the bench.  He seems to sulk when he isn't starting, and that's not a good thing.
But, as I said, for now, he's an average, or nearly so, starter on a reasonable starter.  You want him, sure, but you need to blow my skirt up with a trade offer that also makes my team better and doesn't just give you what YOU want.
BNM