How much of 'the lot' you will have to 'junk', will partly depend on what 'the lot' already is, and what you want to control with it..
IMHO..
If you have MTS2 or less, then you need to thing about upgrading to 'something'.. - Possibly sooner, rather than later, whilst you can still sell it on for a reasonable amount.
As to what to replace it with:
I feel the jury is still out on the MFX as yet. - I do not think there is actually a 'large scale' product (central station) available as yet. Stand to be corrected!!
If you want a cheaper, possibly less powerful CS than the Massoth offering.. How about a Piko? - The software is Massoth, and it is (to all intents and purposes) 'son of MTS'. The Navigator handset even says 'Piko by Massoth' as it boots.
I would expect that as Marklin/LGB release more new products, there will come a time when you are not able to 'get at' every function from other kit.. At that point, you have to decide whether to go down the proprietary route, or buy analogue and fit / have fitted kit compatible with what you already have.
None of the existing stock will suddenly cease to work, AND there will be a market (support and products) for existing equipment for some considerable time.