Got a Ricoh MP6200S (6x read, 2x write/rewrite - yeah damn old), which is pushing past 5 years old now. Did once go on a spree of not writing that well. Tried a normal head cleaning CD and it did the job fine. However, that still didn't stop me taking the thing to pieces and cleaning it properly, checking that the guiding arms for the laser were still greased, etc...
The drive is a sealed unit (or like most attempts to be - even with a tiny layer of foam around where the tray closes on the front of the drive), but that is no guarantee of dust not entering the drive.
A pressurised air can shouldn't hurt anything (as long as its not stupidly high pressure), but remember you are just blowing the dust around a bit and not really getting rid of it.
There are other problems that you can get though. Over time, if the drive keeps getting hot while writing (show me a CD writer that doesn't get a little bit warm doing its job and I will be quite impressed) the mechanics can go out. Technically it should be possible to recalibrate the thing, but I would have no idea how you would do that.
And as other people have said earlier, check your system configuration (ie. DMA mode, conflicts, etc.). Of course you could have a batch of very poor media, but that usually would only effect a write every so often.