My current house wall and ceiling have a heavy knockdown texture and it looks dated to me. Since I am going to paint the whole house so I am thinking change it to light orange peel or smooth finish. However, one of my friends who did a lot flip houses suggested me not to do it since 1) it cost a lot pfn $$ to change from knockdown to smooth especially I have 12' high ceiling. 2) He doesn't trust most of the painters since making the wall smooth need high skill set. 3) The current knockdown texture hides a lot defects, but smooth wall cannot. He also pointed out some of my walls are not flat and it is more obvious with a smooth finish.

I know from cost-effective point of view, I should not spend such money on changing the texture, but I am changing my whole house to a modern look, so just not quite happy with knockdown texture. Any suggestions? Thanks a lot!