With regards glass there is no doubt it will take a pilot accustom to a six pack time to adjust. You cant tell which you prefer until you have been behind glass for at least ten hours and perhaps more.
I can imagine the amount of information availlable from typical glass systems maybe daunting to some, and more daunting is the need to be comfortable with the controls which are many orders of magnitude more complex that traditional instruments. If you are comfortable with computers it probably will not bother you, if you are not, I can imagine some being terrified.
Be it IFR or VFR one of the keys to safe flying is situational awareness. Nothing comes close to the situational awareness provided by a 12" TFT colour MDF or whatever spec it is because at a glance you can see exactly where you are on the chart and if needs must exactly where you are in the IAP. I find it difficult to see how some of the CFIT would have occurred had the aircraft been fitted with a MDF.
To be fair the PDF is simply replicating the six pack and adding a little more information so in itself it probably doesnt advance matters a great deal, but you can paint the map or the approach on most PDFs in a pop up box or beneath the rose which I think advances situational awareness enormously. Also the PDF is more adaptable to pilot grabbing attention by flashing up urgent warnings in a way that is hard to miss.
For those comfortable with glass I think it is a substantial step forward in providing pilots with the information they need in an easy to assimilate form.
On other issues I have no idea whether glass will prove cost effective. I would guess it is much cheaper for a mnaufacturer to install glass in terms of the labour required. Clearly at the moment the systems are more expensive whilst the manufacturers are profitering and paying off their R and D costs but my guess is glass is much cheaper to manufacture. In the marine world you only have to consider how cheap chart plotters are now and I dont suppose the technology is all that different.
Inevitably there is an issue with repairs. It will take time before avionics shops have the skills to repair glass in the field and indeed are authorised to do so. However it should not be forgotten that many of the underlying systems are simply the boxes we are accustom to having on our panels but driven by the keys on the PDF / MDF. For example the GPS nav component of the G1000 is really nothing more than two 430 s. Since the systems are modular swapping certain of the modular components in the field should not be an issue.
IO540 will know better than me but I have a feeling solid state electronics are in the end more reliable and cheaper to repair than something with a whirring mechanical gyro. If that is so in the long run glass should serve us better.