I really think the LC costs should remain where they are now. Part of the joy / challenge of the marines is the way that the various formations and strategies interact. Often, the use of one formation or strategy requires or imposes the use of a second formation to provide battlefield synergy.
As far as I am concerned, LC have two modes of operation, Assault and Deployment. In both cases planetfalling has to be a major consideration because of the significant potential for an AA critical to spoil your day.
If 'Assaulting', you need to minimise the number of formations onboard while maximising the output - hence the Termies+Dreds. Main issue here is that it almost invariably becomes the BTS (Note 1), and you are proposing to put that very close to the opponents army! The use of the two formations yields about the best 'bang for your buck', but as TRC notes, tends to leave the formation stranded (unless you can contrive to let the dreds die . . .

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If 'Deploying', the intention is to land a significant force somewhere it can pose a significant threat, so perhaps 2x Tacticals with transport, or some Devs, Predators and 2x Assaults (or scouts). Here planetfalling is mandated both to avoid losing a significant number of activations, and to make the best use of the troops!
Therefore, IMHO a space craft is mandated when using a LC (especially in a 'blind' or tournament situation), which in turn has already put the costs up.
Note 1.
If you load up a tactical formation to be 525 points you get the BTS with the SC and give your opponent a nice juicy target. If you choose a Reaver as the BTS, you start to run out of activations while putting the SC in a relatively weak formation.