Hmm… this may be considered to be contentious – I don't know…
I think that Lego is best considered as a crude introduction to quantum mechanics, perhaps. Meccano in its present form is going to give you a good background in being a production line fitter, or car mechanic. Come to that, it probably always was. But because it made you think, if you wanted a working result, it was and is better than Lego as a mechanical introduction from that POV.
But I don't think that either of them is truly an introduction to what I think of as 'enineering', as such. The model that the 5-yr old and his father made that 'inspired' that pile of foot-mangling plastic (been there too, NJH – ouch indeed!) looked more like a sensible introduction to modelling to me, though.
So you might wonder what I think that engineering is in this context, and why the neither of these products really make it as a complete introduction. Or perhaps you don't, because you already know from what I've just said. Engineering, and by extension model engineering is, for me, really about the sensible manipulation of raw materials into a usable product or end result, without any particular limitations on the shapes you can utilise, within structural constraints. Yes, you often end up using pre-existing fittings in what you build, but you have to consider their application carefully in terms of what you are building in a way that Meccano doesn't let you (unless you modify it) – the holes are all pre-positioned, and the slots are never quite where you want them…
So are either of these products 'inspirational' as such? No, I don't really think so. What both of them will do is reveal an aptitude towards particular sorts of activitiy. Looking at a giant Lego model inspires you to make one if you don't have the aptitude already? I don't think so.
On the other hand, if you find that you want to start modifying Meccano as a youngster, then perhaps this shows an engineering aptitude, yes! I certainly did, but was heavily discouraged from doing so by the owner of the kit we had to play with. My brother and I started to collect our own, and I still have it all. And a lot of it is bent considerably out of shape, obviously. The slightly perverse thing about this was that it did confirm my bro's desire and ability to become a mechanical engineer – but he ended up machining plastic for a living, which he was consumately good at. But that all came to an untimely end nearly 40 years ago, unfortunately.