Not really. Its just better out of sight I believe? I may just change the aerial for a more up-to-date one and replace the exterior coaxial cable as a matter of course?
Generally, you'll stand a better chance of getting a decent TV reception if your aerial is mounted outside, unless you happen to live in a very strong signal area. If all your neighbours have external aerials, then that might be the way forward.
If you're only feeding one TV, then try and get one continuous coax run from aerial to the outlet because every break or join (eg. your unused splitter) will lead to signal loss. Use modern, good quality, foam-filled (not hollow) coax for the cable run and a good quality fly-lead to connect the TV to the aerial outlet. Making your own from excess coax is likely to be a better option than a cheap one from the likes of Argos or Ebay.
If you want to feed more than one TV, then it would be sensible to use a (powered) distribution amp/splitter in the loft to minimise signal loss. A masthead amplifier is another way of improving and distributing a TV signal but it sounds like you live fairly close to your transmitter, so this might not be needed.
If you put your postcode and house number in the checker on
www.freeview.co.uk then click on 'Detailed view' at the bottom of the channel list, it'll give you a bearing in degrees so that you can point your aerial in the right direction. I doubt a phone will be accurate enough - could you borrow a compass ?
Some TVs have a built-in signal strength meter so check your TV's set-up menu - this would allow you to adjust the aerial to give the strongest signal. Get help with this or take an old, small TV with a similar feature into the loft.
The site will also give you an indication of what the signal strength will be like for the various muxes and what 'group' (eg. type of) aerial you will need. Note that this may change in the future. There have been changes to Freeview over the years (including some as recently as a few months ago) and it's possible that your current aerial is no longer the right type and/or that a different type of aerial will be more suitable.
Another site to use for this info (and more) is
wolfbane.net
As your new TV will have a Freeview HD tuner and you haven't mentioned problems with BBC One HD, then you should be able to watch channels 1-5 in HD without issues as these are all broadcast on the same mux.