Update to my last post: the Timberland Boot Kit helped a bit, with a few cycles of brushing and cleaner and then conditioner. But what ultimately helped most was dried bread. :
Men's Timberland® Premium 6-Inch Waterproof Boots
Dry Cleaning Kit
Timberland Footwear Dry Cleaning Kit (Brush & Eraser) For Nubuck & Suede Cleaner For Shoes and Boots - Walmart.com
Timberland Boot Cleaning Tutorial - YouTube
Timberland Boot Care Kit - HDZ0001-BOOT KIT
Sof Sole Boot Care Kit with Waterproofer, Cleaner and Brush : Health & Household - Amazon.com
Timberland Shoe Care Leather and Suede Protector Dry Cleaning Kit Suede Brush | eBay
Amazon.com: Timberland Boot Kit No Color One Size : Clothing, Shoes & Jewelry
How To Clean Timberland Nubuck and Leather Boots at Home
Timberland Fit, Care And Size Guide | Buyers Guide - AllSole
3 TIMBERLAND Saving Hacks - (Tested) - How to Clean Timberlands Boots - YouTube
How to Clean My Timberland Boots | Timberland - YouTube