Regarding new spells, the Spell Treasury also converts a goodly number of spells from the Books of Hallowed Might that Monte wrote for 3.0. If you don't have those, then yes, there are new spells in the ST. Many of the spells from the
SRD are significantly changed, especially with AE's lack of alignment, and the necessity of adding heightened and diminished effects, and various racial descriptors, which can give things a new flavor. Most of the spells also have new names, many of which are flavorful, but indicate more about the fluff than effect (Discern Lies becomes Gaze of the Sibeccai, True Seeing is Lion's Eye, Brambles is Cluatta (the Litorian word for punishment) etc.) While there is an index cross referencing the new names with the
SRD names in the back of the book, I've found it somewhat annoying to convert.
As far as supplements go, none of the AE books Malhavoc put out are outright bad. Mike Mearls did most of the design work on them, and his stuff is always a mix of brilliance and terrible disappointment for me, but YMMV. (Obviously
WotC liked his work for Malhavoc enough that they hired him to work on core D&D and to help design
4e, since he barely finished Iron Heroes before leaving Malhavoc)
Mystic Secrets: The Lore of Word and Rune presents a lot of new material despite it's short length. In addition to new spells and runes, it presents variant Runechildren and their opposite number, the Heralds of Annihilation, Rune weapons and runic templates that can be added to existing magic items, ritual magic that any character can learn, and several interesting magical locations and guidelines for making your own.
Transcendence expands on the idea of Evolution with evolved levels centering on evolving one of the six stats (Str, Dex, etc.), introduces a couple of new materials (daelren and Tylonian crystal), details the Totem Speaker base class (sortof a druid/bard that must be read to be believed...it's just exceptionally weird) and provides additional crunch for every core class in AE in terms of feats, PrCs, replacement levels, class specific items, new witchery manifestations, etc. In particular, the fighting classes gain a lot of new options from this book, balancing out the power creep the AE casters experience with Spell Treasury somewhat.
Ruins of Intrigue is a weird product. Half adventure, half setting book, it details a single city and it's factions and more or less presents the place as a huge sandbox giving the DM ideas rather than statting everything and giving it a linear plot. It has monsters and sample encounters and NPCs, and some really neat fluff.
As mentioned above, Legacy of the Dragons is a really nice bestiary, presented in a format that
WotC would later emulate in
MM 4 and 5, with sample encounters and lots of fluff for each monster. Some of my favorite monsters lurk in this tome, many of which are responsible for the most memorable moments of the first campaign I ever DMed. In particular, the Valloreans are a great villainous race that recaptures what made the drow scary before becoming watered down and mixes it with a dash of the Cthulhu mythos and Chaositech. Definately some of Mearls' best work.
Robert "One Man's Opinion, Formed By Seven Years of Play and Six of GMing" Ranting
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