I test drove a couple of D110's before I bought my 1st Gwagen in 2000. I thought the 460 series 300GD that I ended up with was a much nicer and better built vehicle from a newb perspective. The Gwagen that I got was nicer than many of them with the factory Recaro seats, and was a nicer drive and more comfortable than the NAS Defender 110. I have since traded to a G500 (2002) sold originally by MBUSA and appreciate the available power (300HP) much more. The Pre-2002 vehicles have the same motor as the MBUSA truck but with less drivetrain and stability management, an advantage that makes them some of the best Gwagens ever sold. With the center diff locked they are a very similar beast though. Also, the early G500's have the benefit of a manual transfer case shifter. I looked seriously at a Europa G500 before buying used in 2008. However, all of the modern Gwagens are complex electronic vehicles and I feel that access to repairs is more available with the MBUSA trucks. Either way, it is a huge step from a D90 in a positive way. I do like the Defenders though, very classic style, probably the basis for the G design.
A 460 Gwagen is a great trucks also. The gassers are a bit thirsty with fuel and the diesels are a little slow on the on ramp, but on the trail they are all about the same, including your D.
1999 Mercedes Benz G500
1989 VW Syncro Westfalia 2.5
1978 VW Westfalia deluxe