Smith was frustrating and brilliant in equal measures. He was far too cautious at times, leading him to make the wrong pass or the negative move, rather than being positive and finding the man up front or on the wing. As you say though, he kept the team ticking over.
Wes was the grafter in the midfield, something we can all appreciate - Would have loved to have kept him, but there's many of them about, probably on cheaper wages too.
There's a clear difference but the partnership this season was key to our success in some games, but I believe that it was also key to our downfall in others. Both players reluctance to move forward and kick on at times drew us into a deeper style of player (similar to what we had experienced the season before under Dickov) - something which probably cost us on a few occasions. There needs to be a clear emphasis on our play this coming season, whilst it's imperative that we defend well, it's hard to get anything more than a draw or a 1-0 win whilst both your central midfield players are sitting in the holding position, waiting for the wingers to have an impact.
Losing Wes has indeed been a blow, but not something that should massively affect us this coming season. Losing Smith as well would be more devastating or would be harder to replace, especially for the low(ish) money that he will be on - you can't pick up players of Smith's quality easily.
I think it's a case of you don't know what you've got until it's gone with Smith, many people underestimate his abilities and what he does for the team but we'd be hurt if he went, especially having to find two quality central midfield players, instead of simply finding a partner for Smith.