Hdr it...reduce all the settings and layer in p/shop. No need for neutral grads this way

Of course 3 exposures are preferable to the one RAW with a stop or two difference in the software option
If you shoot in RAW then via layers you can replicate nearly all filter effects anyway. ND filters bring more image information into the photo...think about it. Shooting multi's (you have this luxury with landscapes) can do the same thing....in fact more.
If you are using film then filters are a Godsend.
Did you shoot in RAW Pete ?
Email me the file bud.