First off, no right or wrong to this discussion, just people with different views and preferences.

So let's say in the same development/master plan, there is existing completed units sub-sale, and around 5 minutes away by car, the developer has new project launch which will require you to wait < 3 years. Subsale unit is also "outer", nearer to the main roads, and new project a bit more "inside". Just imagine it is 1 extra traffic light for the new project to the main road.

20x75 for RM500k nett, completed 10 years ago
20x70 for RM600k, new project, RM540k nett after discount etc.

Let's assume, in terms of layout, both are 4R3B, can park 2 cars in tandem by default. Slight variation in terms of the floor plan but basically comparable. Of course the old unit has a bit more usable space and 5 feet extra land.

You can see, touch, feel the subsale, you like it, obviously it is a bit old, paint needs to be refreshed. Biggest benefit is you know what exactly you are getting, and price wise it is cheaper by RM40k. And you also seen the neighbours and let's say you are happy with them -- no big dogs barking, don't have neighbour with 6 cars parking the whole road.

Which would you prefer to buy and why?

Double the price then
Arbitrary.

It’s more to find out sentiments.

So far it seems there needs to be substantial savings versus new project.

Unless the old unit is very well maintained and/or refurbished prior to sale.