the reason I say it is overplayed is because plastic lenses are every bit as good as glass, except for scratch resistance, so that is not a big cost factor.
What??
No, it is not. Where are you cherry-picking these unqualified statements from?
Modern day spot meters use multicoated glass at both ends to deal with reflections (many also have dioptric correction lenses built into them), and most again have a threaded front to take a filter (e.g. Sekonic L758D has a 40mm thread) and/or soft or rigid hood e.g. spot meters can take a polariser, 81B or other filters instead of manually entering the FF into the meter). As Vaughan mentioned, scratches on plastic would quite rightly reduce the useful lifespan of the meter, secondary to the main problem of making viewing an irritation rather than something one needs to concentrate on, and introducing flare in specific lighting situations. There is a big and very noticeable difference between squinting through a plastic lens compared to a corrected, multicoated lens that is specifically designed for the purpose and not as an afterthought.
With care and attention, something I would expect to give my light meters anyway, there is little reason to worry about damage to a light meter, but it would be far easier to replace than dropping something that cost nearly a grand based on inflation.
You wish. 
Could be true thought for people living in a mollycoddled bubble who never venture out of the front garden poking around the roses, but for people active outdoors every day in adventure and endeavour, damage will come and go, unseen or unplanned (sometimes both!) as part of daily life, no different to your car being hit by hailstones on a seemingly beautiful blue-sky day. Shit happens.
Really, damage to a light meter is
very common. Broken invercones, or sun damage to invercones (resulting in spuriously inaccurate readings) are two very, very common types of damage - a broken invercone is easily replaced in-field, but a damaged and blighted cell behind the invercone is a much more serious set back. Light meters are an investment, and precision measuring instruments with high quality glass lenses to be used with care — something I drum into my workshop participants when they first come to grips with an L758D — intimidating as it looks, it really is not, an 40mm UV filters are placed on these (loaned) meters for the duration of the workshops. My first L758D drowned when I tumbled into the briney interstate in 2011. Having to rely on the TTL meter of a Pentax 67 was eye-opening, and shows just how much better and more refined a skilled application of a light meter is by comparison. But it seems few people will see that, they're more interested in pennies and plastic!
BTW, spot/multispot/incident meters use two separate, independent meters, calibrated to that specific and very, very accurately to the angle of the meter. That spot would be quite difficult to view if the optics was plastic, to say nothing of those wearing glasses that would see chroma and fuzz. Thinking that somebody, somewhere, will come up with a $50 spot meter with plastic lenses defeats the purpose at the starting gate (economics does not permit you to pay a tiny bit and get a lot!), and such a meter would only hazard accuracy rather than attest to it.