There was a list posted somewhere of his signings, and of the ones that were actual long term signings, TWs hit rate is actually good. It's the late, free transfer dross signings (I'm looking at you, Denny/Fallon/Morgan) that struggle.
Clark can replace Mannus, he's not as consistent, yet, but either way he's at a stage where he needs to be first choice to improve.
McMillan was signed to replace MacLean I think, as MacLean has suffered badly this year. It's hard to judge TWs striker signings as he's never actually signed anyone to be first choice, it's always been a signing to play second fiddle to Maclean. Kane has had a good four games but it remains to be seen if he can maintain that. Regardless, MacLean only has five league goals, a feat we should get from McMillan and Kane, plus any other striker.
Biggest issue by far is if Murray Davidson leaves, he's a bit of a one off and I've no idea how we find a direct replacement. If he leaves I suspect we'll be changing our style a bit. We could muddle by with Craig/Wotherspoon helping out in there, but the decision to let Paton go to bring in Willock will look a bit foolish if Davidson does go, despite how low I rated Paton.
My biggest concern this Summer is Steve Brown. There'll be a lot of wages freed up, and if he'd just release a bit more we could afford extra quality which increases the chances of a successful signing.
tl:dr TW + Money = Good, TW + no money = bad