Hello Porridge. I don't know a huge amount more than you, but for what it's worth, here's the result of my investigations into your questions on Google:
The "R" format disks are cheaper to buy and a little more widely compatible on on standalone DVD players than the "RW" disks. Otherwise as you say the only difference is that you can't erase and re-use the "R" disks.
As for the difference between + and - .... there are apparently three competing DVD Recording standards:
(1) DVD-R and DVD-RW (the formats with a "-" in the name) and
(2) DVD+R and DVD+RW (the formats with a "+" in the name) have similiar features. Both are compatible with many standalone DVD Players and most (read-only) computer DVD drives
(3) DVD-RAM has much less compatibility but better recording features.
(1) The formats with a "-" in the name were originally incompatible with standalone DVD players, but compatibility was added to the format later. Confusingly for us beginners, there are two different ways you can record on these disks: so-called "Video" mode and "VR" mode. "VR" mode gives you better editing flexibility after recording - but the disks are then less compatible with standalone players.
*DVD-R is non-rewriteable & compatible with 93% of DVD Players.
*DVD-RW is rewriteable & compatible with 80% of DVD Players
These formats are supported by DVDForum (
http://www.dvdforum.org)
(2) The formats with a "+" in the name were designed from the start to be compatible with ordinary DVD players and computer drives.
* DVD+R is non-rewritable and compatible with 89% of DVD Players
* DVD+RW is rewritable and compatible with 79% of DVD Players.
Because there are no confusing recording modes, you don't have make trade-offs between compatibility and flexibility, according to its backers, the DVD+RW Alliance.
http://www.dvdrw.com
(3) DVD-RAM
* DVD-RAM has the best recording features but it is not compatible with standalone DVD Players. Think more it as a removable hard disk.
This format is also supported by DVDForum.
Finding something on Google definitely doesn't make it true, but that was the best I could find. Perhaps other better qualified people will be able to improve on it ?