Ha, I think anyone who suggests Mulberry bags look cheap obviously doesn't have any experience of them!
In terms of the older styles, they don't look at all cheap and last for ages! In terms of the newer styles, again there's nothing cheap about them at all but they are arguably not made as well as the older styles. I'd say the leather is still just as good but with some bags, the craftsmanship isn't quite as it used to be. For example, many have reported problems with the Alexa - I have one but no issues so far - but there are certainly more reported problems with the later styles.
As an owner of two Balenciaga bags, one Marc By Marc Jacobs and an Alexa, I'd say I am more careful with my Alexa than any of the others. Considering the Balenciaga bags are by far the most expensive, I never feel wary of them when carrying them, even in the pouring rain. On that basis, I'd say Mulberry bags are pretty durable - depending on the leather - but shouldn't be thrown around carelessly or exposed to rain on a regular basis. Some owners treat their bags to protect them from rain. I personally don't.
Note that I am not including the delicate Mulberry bags in my description, ie. the sparkle tweeds, which are VERY high maintenance and require a lot of care!