That’s a difficult question Rob. it’s taken me a while to get the gear that I do have and my mantra is “if it ain’t broke don’t fix it”. I upgraded to PT 9 from 8 when it was released, then they released 10 less then a year later and 11 after that. Avid is sort of a love hate relationship for me. I’ve been working with PT since version 5, hell I remember when they upgraded to actual “Stereo tracks”. I know that dates me a bit but you work with what you know and are used to. That doesn’t mean I can’t work on other DAW Platforms, a console is a console whether it in the box or not I just go with what I know and am comfortable with.
Upgrading or buying a new piece of gear or software really should be done when there is something that your really know you could use. Like for me the Izotope RX3 suite of noise reduction and audio clean up plugins. those things are freaking amazing. I just finished up the post production and mix on a local Documentary film which was filmed in the Ecuadorian Amazon. Using the spectral analyzer took some getting used to but OH MY GOD was it useful in taking out crazy stuff like insects and chickens (yes I said Chickens) interfering with dialog. and the De-reverb plugin was very useful as well.
On the writing side of things, East West have an excellent deal on their “composers collection”. Best $900.00 I ever spent. you should totally check it out, though the Drum samples for me don’t work as well as I think they should. For drums I use the “addictive drums” plugin and sample adpaks. The company has put in a lot of work into the adpaks and they sound surprisingly natural. I’m not a drummer I’m a guitarist and a vocalist and that said, having a base groove from which I can start writing is really important. I guess this sort of answers your question too Dante.
You also have the bane of any type of software upgrade. Compatibility with your operating system. for instance I work with a composer who is using Guitar rig 3. I have Guitar rig 5 and they are not compatible. so you have to find workarounds like printing the sound for mix etc…
My opinion is find what you like and stay with it.