Right to Abode in expiring passport

Apologies in advance for possibly raising a question that has been asked (and answered) before. I had a search, but I guess no two people have exactly the same circumstances. So here goes:

I have lived and worked in the UK for 8 years on my Australian passport with a certificate of entitlement of the Right to Abode. However, since my Australian passport expires in June 2016 (now just 4 months away), I have for a while been looking at my options.

On the one hand, I could have renewed my Australian passport and then sent that off for renewal of Right To Abode certificate. It's annoying that you can't just transfer it, and have to go through the entire process again (including the "can take up to 6 months to process").
The other option was to apply for British Citizenship by Descent after the 2010 law change about being born to British Mothers before 1983. Prior to this law change, I was limited to just the Right to Abode, whereas my younger brother (born post-1983) has previously acquired his British citizenship.

So anyway, I went for the second option, and sent off my documents and UKM form in November 2015. I figured the "can take up to 6 months" with this option too when deciding to send off then, with no travel planned for a couple of months. I would just need my passport back before my next trip.

So now to my current position, and reasons for asking for some advice or guidance.
I have my documents back. My application for citizenship is pending, but "due to exceptional circumstances will take longer than 6 months". So I think any hope I had of having British Citizenship (and then a British passport) before my Australian passport expires is gone.
Just to make things a little trickier, I have trips out of the UK coming up in late Feb, late March and late June. Ideally I want a new Australian passport before the March trip as by then I'd be falling under 3 months til expiry, and Spain might not let me enter!

If I renew my Australian passport between Feb and March I will then obviously not have the Right To Abode certificate in it. It will be in my old Australian passport, which I assume becomes expired as soon as I have a new one?
So now I am worried the UK Border Agency will deem me to be entering the UK as a visitor when I use my new Australian passport, which would impact me work-wise and limit me to a 6 month stay?
I could show them my old passport, new passport and a letter saying my British Citizenship application is being considered/processed - would that be of any benefit?

The Right to Abode certificate itself is confusing. It does not confer the Right to Abode, it merely indicates I have it. Yet you must renew it in a new passport, what do people do while the renewal is pending? Are they grounded from travel for up to 6 months?

Just as an FYI for anyone going through the UKM application process. Having posted my application on 11th November 2015, I have today received my letter saying my application was successful. So I am pretty relieved.