Not the greatest panel but a popular DIY choice. As with a lot, the older ones seem better as they do last. But have less functions. A 9100 scanny is bullet proof but you need an engineer to change the user code. What a fantastic idea :D.
I digress, as you want to keep it I would change the PIRs as you say. The battery in the panel ( I know repeated you, force of habit to recommend this, for others reading I have kept it in) and a NEW external sounder. An old one will look tired and may have others will ill intentions think the system is either dead or dying as well. You are going to have to go up to change the battery anyway. You may find the newer ones have almost the same footprint so changing is easier ( No more drilling needed).
So go ahead as you intend but do please get a new SAB rather than the battery. You know it makes sense.
I dislike the Veritas because when they first came out the rep had a "Aircraft Briefcase" with the panel installed and toggle switches to show how it worked and programmed. It did have a lot of features for its price at the time I do admit (And faults and quirks as we soon found). But the main bugbear was the fact when he powered it up it went up in a puff of smoke, yes, up in smoke. Blew up in the briefcase display unit. He sat there shocked ( Well he was promoting a new product) as did my manager. Two other colleagues and myself were falling over laughing our heads off.
I have had stuff blow up on me as we all have straight from the box, but to have an audience and promoting how well it has been tested must have been a tad embarrassing for the rep :D
PS: Do be careful on the ladder as you mention it could be difficult. Safety is of course paramount.
Good luck
Alarm
May 2014