The Dalyell program is basically a worse version of the Talented Students Program which it replaced. I actually like TSP, but I'm not as sure about Dalyell.
Can someone tell me what the actual benefits of joining are or if there is any? What are these accelerated and advanced units that are available to the Scholars?
The "accelerated" and "advanced" units are really just you being more likely to be granted the ability to take 2nd and 3rd year units earlier. Personally, unless if you're very good and confident, I wouldn't recommend it, even though it might sound kind of enticing.
Do you actually get a professor as a mentor, and how do they 'mentor' you?
Yes. As a part of Dalyell, you get to do these project units (equivalent to the old TSP units, which I still get to do), where a professor proposes a 1-on-1
or 1-on-small-group project or course throughout the semester. These count towards your degree and major, and from both experience and the opinions of other students, these are pretty good, and probably the best part of Dalyell.
For example, I entered into a 1-on-1 reading course with a lecturer of mine last semester, and while stressful, I ended up learning a lot and we've decided to enter into another one next year, which will be much more research-based. The progress I've made with the subject area will very very likely end up as a part of my honours thesis, which is very helpful. Moreover, doing these courses allows me to skip a third year stats course, which is very nice.
Other students do projects as a group, and they may have to present their project and findings.
So generally, these project units are informative, very educational (often more than the usual courses), and fosters close connections with your lecturers, which is definitely useful for honours/research opportunities in the future.
You can take these project units at any point in your degree. I decided not to do any back in first and second year. I think third year is the best time to take them, since 1. they contribute to your major, and 2. the projects/courses are much more relevant to your honours and future research.
So if there is a reason for me to do Dalyell, this would be it.
Does it actually help you study or get better grades?
Often, people take these project units on top of their normal workload (as I did), and so it usually makes your semester even busier.
However, what you can also do is to take these units (in third year) to substitute units of your major that you don't want to take, which I'm also doing.
Also, depending on the nature of your project/course and your supervisor, they might give you very high marks for these units. But this depends on how chill your supervisor is.
I don't really care about the employability and leadership part; I am only interested in the academic part. Hence, are there even any academic benefits?
Academic benefits? Yes - these project units are probably the best thing you can do as an undergrad (within semesters) to prepare for research.
I know a few students who are publishing as a result of these units. Although realistically, this is pretty rare and you shouldn't expect it.
Also, I think I heard something about how with Dalyell, you automatically get $2,000 scholarship for exchange, should you decide to go on one. I personally don't think this is all that great, but maybe that's just because I don't like exchanges.
So all in all, Dalyell's main benefit is the ability to initiate into project units with your lecturers. You should purely decide on this point - whether you think it's worth the extra effort.