The addition of a foam mat will certainly make a difference to your insulation from ground cold.
I'm less convinced about a silk liner. I do use one, mostly to help keep the bag clean, but over the years I've come to think it only adds a degree or two to the warmth. I'd be more inclined to supplement the bag's range simply by sleeping in my baselayers or wearing my other dry, warm clothes (down, primaloft, fleece, whatever you'd be carrying anyway) inside it through the night.
But I'd definitely say do it, get out there and give it a go - autumn colours, frosts, dark night skies - it can be a brilliant time of year to camp
In my avatar I'm wearing an old original Aspira from 2000, which I used for all my winter activities for 10 years (including annual hut-to-hut ski tours in Norway). In those days the pump liner was a heavier fabric, and that smock was very warm.
In 2010 I got a Velez Adventure Light (I've also got a Velez and an Alta II, all since Paramo reduced the weight of the pump liner a good few years ago). I find all these a little less warm than the original Aspira but all much of a muchness warmth-wise. I can't see any reason why the current Aspira would be noticeably different, perhaps only the extra layer of fabric where the double chest pocket arrangement goes across.
That said though, I question your starting assumption that "the Aspira would provide better protection in harsh conditions". Since 2010 I've used the Velez Adventure Light as my winter jacket, in fact I haven't worn the Aspira since I got the VAL. It's dealt with all my ski touring, Cairngorm snowholing, etc., often in atrocious conditions, and I find it every bit as protective, especially the hood which performs just as well in a blizzard as the Aspira (and better than the other jackets I mentioned). The VAL is more versatile across varying temperatures, and a lot lighter and less bulky if I ever want to carry it rather than wear it.
IMO the reasons for an Aspira over the VAL are not about protection per se, but would be if you need a more rugged outer for your activity (I've not trashed mine in 5 years, but I'm not climbing. And there's the option of the Velez Adventure). Or if you particular like/need the extra pockets on offer with the Aspira - I do occasionally miss those but clearly not enough to choose to use the Aspira.
Adrian, I've not got anything to do with this particular meet, but you should be fine. Meets like this one organised on public OM threads are generally open to all, and the link in the first post to the climbing barn states that it sleeps up to 30.
I expect Maria will show up to confirm that at some point, but if you're up for it then add your name to the list.