It's certainly a balancing act between retaining squad unity whilst also looking to improve. I always think back to how Newcastle were heading for the league title but brought in Faustino Asprilla and it appeared to upset the apple cart.
But fundamentally the attitude should always be to look to improve, and take advantage of the opportunity to recruit players we perhaps might not otherwise be able to, if we weren't in the promotion mix.
Also it's not as if we're 15 points clear at the top! Fine margins could make an enormous difference to our season.