The old "mortgage vs investment" predicament.

I've seen a couple of these threads already but none that quite fit my situation.
I'm 28 years old and I own half an investment property with a mortgage of $246000 at an interest rate of 4.75%. This is neutrally/barely negatively geared costing me $30 per week.
I also own an apartment with my partner with my half of the mortgage being $186000 at 4.5%. We have no intention of selling this property and if we were to rent it out it would be neutrally/barely positively geared, making approximately $20 a week.
Down the track maybe 5 or more years from now we might look at purchasing a house together.
For the immediate future I want to set up a mutual/index fund portfolio, which seems to have a long term average of around 10%.
I suppose the question is what do I do? My biggest concern is what do I do when interest rates go back up? Will it be better to have an established, diversified share portfolio which I'll contribute to on a regular basis OR to really knuckle down and pay off my non-tax deductible debt. Or both?