In an ideal world, you get your players you definitely want to keep, on contract early on for next season. Tell the remainder of the squad, to earn themselves a contract - that incentive should then spur them on to play better.
Southwell may also get the chance to go pro like Miller, either lower end League Two or higher end Conference. Would Paul Hurst admit a mistake and re-sign him? I can't see Lincoln offering much more money than us, in their current financial woe. Scunthorpe are too high, surely (unless they take a punt on him, like Bradford did with Hanson from Guiseley?). If Southwell scores 25 by the end of the season, then surely he's a more attractive proposition due to his age, than Miller?