They obviously have players that they would like to have - the "significant" bit to me means actual players that will walk into the first team not just this season but potentially in the Championship. If they came then the players they replace would either revert to squad (therefore making the squad stronger) or move on, giving some of the younger players the opportunity to become the sqad player and so on....
As to them doing their best or don't see the real need to get players in bit - I think they are probably doing their best and and are always looking to improve the squad but if the players are not out there/available then they will keep what they have got by default.