It is almost impossible to answer this question in the abstract, as unfortunately you give no indication of what you propose to study, and of where you are applying.

In normal circumstances, neither of the two motives for pursuing a degree course that you quote would be the first priority for an admissions tutor. This is particularly the case for over-subscribed courses at the most competitive universities. The crucial determining factor is the applicant's academic record; hence grades (GCSE, A level, etc) are critical - including for mature student application. They will also want to ensure that you have a source of funding, to pay the tuition fees, and of course your living expenses.

For some courses of a vocational nature - such as medicine, nursing, law, architecture and many branches of engineering and applied science - there are natural connections with a future career, and the admissions tutors will expect to see links made between the course applied for and the future career in the UCAS Personal Statement. Most courses are not however of the vocational variety, and so career aspirations are not seen as particularly important. Certainly in all such cases they are unlikely to influence the final decision - relevant work experience already completed might be rather more important.

On the personal development front, it is taken as read that students develop both academically and socially while at university. So the secret here is to stress in your Personal Statement a number of the skills you have acquired and are keen to develop further, always where possible citing particular examples of activities that have required the acquisition of skills. Particularly important are any relating to time management, the ability to recover from setbacks, leadership, teamwork, communication, IT and contribution to the welfare of the community.

That's as far as I can go in the absence of more detailed information, but I hope this helps.