Edit: This replacement is still working as of 28/12/2018.
It seems to have failed after an unexpected very hot day. The touchscreen didn’t work except for incorrect (touched the bottom left on one screen and it pressed a button at the top right). Similar to this https://www.youtube.com/watch?v=wnCOUHyiPeg
The LCD and all physical buttons worked perfectly.
I researched online and attempted the circuit writer fix (very good guide here: https://snapguide.com/guides/fix-the-touchscreen-in-a-lexus-is350/ and more info here: http://us.lexusownersclub.com/forums/topic/69937-repaired-navigation-touch-screen/ ) however, if like me, your skills are not great with breaking small bits of glass and patching up the connections – or your break in the circuit isn’t right near the edge (unfortunately can’t tell without trying), I’d suggest forgetting it and replacing the digitiser.
The cost of the circuit writer pen was $40AUD, and as I didn’t have a multimeter handy, so bought a cheap one for $10. Jaycar have both of these items.
I ended up umming and ahhing about buy an exact replacement of my digitizer which is the same type as in the guides (has a triangular kind of shape). However, these replacements were $120-$185+ and 3 week ETA.
More info for other success stories here: https://www.reddit.com/r/Lexus/comments/29spwr/my_2007_lexus_is350_touchscreen_has_been_dead_for/
I looked online and asked ebay stores questions, but no-one really wanted to admit (or risk saying and it not working) that the cheaper screen would definitely work. I found a video on Youtube that showed a guy replacing my type of screen with a cheaper version, so I bought one. Cost around $75 inc delivery and took 6 days to arrive (bought on a weekend). I’d link to the store, but it seems he no longer sells them. You can buy plenty from China through ebay, but they’ll take about 3 weeks to arrive. They are however a fair bit cheaper.
The video https://www.youtube.com/watch?v=g_IXpgrQpBU shows pretty much the exact old and new digitisers I have and used. I also broke the old digitiser glass but made sure not to damage the LCD. I used a heat gun on medium temp going over the edges only, slowly by slowly and cutting under it with a blade.
I then used high quality double sided archival photo tape around the edges after carefully cleaning it off with a tiny amount of methylated spirits and a cotton bud, then scraping with the blade.
Once replaced, it works perfectly.